310XT is most everything Garmin says it is
I felt compelled to write a review, because I am troubled with what numerous other reviewers are publishing. This is the best watch of it's kind I have owned, and as long as a purchaser grasps what it does, and it's limitations, I think they will be more than satisfied. It may be that this watch will not meet their needs, but it must not be a cause to deliver a poor rating.
I have owned the Forerunner 305, the 201, the Timex GPS and a Polar, so I have years of experience. Since I do triathlons, I was most looking forward to the waterproof controls, and 20 hour battery. The charger is a bit funky design, but for me it seems to work just fine. My battery has been lasting at least 16 hours--I haven't tested it further before recharging. One issue that I had with the 305 also, though: the watch must be TURNED OFF while you are charging. If not, as soon as you disconnect the charger, since the watch is ON, it will start out "discharging" (as it does commonly while it is on. I have been caught various times with a depleted battery on my 305 because of this quirk--I think the watches will have to be programmed to mechanically turn themselves off when the charger is connected).
I have employed the new watch swimming, biking and running and hiking, and I am pleased with the performance for each sport. One reviewer pointed out that there must be a "swim" mode--I agree, but I think Garmin may have averted that mode because the GPS does not work well in the water. Several reviewers complained when it comes to that, nevertheless Garmin does write on their internetsite AND in their manual that the GPS does not work well in the water (I don't recognise that I would blame that on Garmin--probably the engineering is just not there yet--besides, GPS signals do not penetrate water.) In fact, I did NOT get an exact GPS distance reading for open water swimming, but it did map my COURSE correctly, even though with a lot of zig-zags (I know I can't swim in a straight line, but I am not THAT bad).
The biking portion works great. The Garmin matches pretty almost with the distance measured on my bike computer (I don't have the Garmin bike sensor--I want that and the quick-release mount for my next birthday). Of course it likewise tracks speed, altitude, heart rate, etc. (I applied the heart monitor strap from my 305).
Running works well also, fundamentally same as biking though I do set up the display screens differently.
Other, utile new features I have noticed:
1. The watch locks onto satellites more quickly than my 305
2. The watch vibrates, though I wonder how this affects battery life. For instance it vibrates each lap (if I set it) so I know I have finished an autolap without having to look at the watch.
3. The software is more refined (lots of little fixes. For instance the settings function lets me know what sport mode I am in--although I think this could still be made requiring little effort and less confusing. And the time zone may be put on automatic--I always wondered why they couldn't do this before--the watch knows where it is for gosh sakes. And there are extra habit screens if you want them--statistic hounds take note.)
4. Wireless info upload. Very nice! Their new "Garmin Connect" internetsite is likewise gorgeous useful, and the data may be uploaded directly to the Internet.
5. The 310XT is not much littler or lighter than the 305 (according to the specs), but it FEELS MUCH littler and lighter.
6. There is a progress bar for the battery charging. I would like to be competent to see how much time is LEFT in my battery--I wish Garmin would add this.
In summary, I think this is far and away the best GPS watch Garmin has made, and is peculiarly suitable for triathletes (despite the swimming issue). You DO need to become accustomed to using the watch. Although I do not think it is hard to use, you SHOULD read the manual. At least you do not have to keep RE-reading the manual like I do for galore other gadgets. I do think this watch is way overpriced, but I am a gadget freak, and I'm sure the price will come down over time, like it did for the 305 (which is a outstanding deal, now, btw, if you don't need a 20 hour battery-life and a waterproof stopwatch 
Somewhat Misleading Advertising to Triathletes
This device has been represented as a triathlete's watch and the initial swim proof GPS watch. If you watch the video from Garmin or see any of the advertisements, Garmin leads you to believe that this watch will gather dependable info for all 3 multisport events. It is reasonable for an individual to assume this watch may be worn in a race and gather GPS info in the water, since, of course, SWIMMING is the introductory event in a triathlon.
If you are giving careful consideration to buying this watch realize the following:
-This device does not gather usable info in the water, amount of time (other than time, which any $20 waterproof watch may gather in a much littler form factor). No heart rate info and altogether unusable and inaccurate GPS data while in the water.
-There are preset modes for run, bike, and "other", in which "other" shows a person on skis (explain that one?). They deliberately omit a category for swimming, in spite of promotion that this watch is for triathletes (see the photo I added under product photos).
-You will need to buy a discerned quick release kit if you want to use this watch on a bike. It does not get exact selective information on a bike if you are wearing in on your wrist. It automati pauses, then unpauses for most of the time I am riding if I wear it on my wrist -- even if I have it set to only automati pause when totally stopped. The quick release kit IS NOT the more mutual one for the 205 and 305 Garmin 010-10889-00 Forerunner 305/205 Quick Release Kit, so do not buy that one. They have made a new one for this watch and most places do not have it in stock yet. As of the date I am writing this review, it is not yet available on Amazon.com. Go to Garmin's web site and look under the accessaries tab for this watch. You will see a dissimilar model number. I have confirmed this with client service. The part number for the proper quick release kit is: 010-11215-00. Google it.
-If you want foot cadence or the capacity to track distance indoors and assume you get it for spending $400 on this device, think again. You will have to buy a discerned foot pod which costs $80-100, depending on where you buy it (earlier Garmin Forerunner watch kits included foot pods). Garmin Foot Pod SDM4 (ANT+)
-The watch is huge and sits high on top of the wrist (they packed 20 hours of batter life into this watch), so to wear it under your wetsuit will let water in the wetsuit, or you will have to wear it on top of (or crammed in front of) the wetsuit, which will not grant you to remove your wetsuit without firstborn removing the watch (thus adding time to your transition and sort of negating that whole "triathlete" angle). You may see a photo of this watch on my wrist beneath the photos section of the product.
-There is no way to turn off GPS tracking for only one of the 3 events in multisport mode. Therefore you will always either have faulty GPS data recording for the swimming mode (or, actually "other", since there is no "swim" mode, as antecedently mentioned). I have called client help and they affirm this. Their solution was to turn off GPS while I am swimming, then reset and manually commence a new timer and mode for the duration of transition 1 for my bike event. I'll let you be the judge of how to take that advice.
So, in conclusion, if you want to setup this watch for a bike and run, and want the capacity to wear the watch in the water before hand (and no start out it unless you want galore faulty distance data included), you will need to buy:
$400 - the Garmin 310XT with HR
$25 - quick release mount kit (for wrist and bike) (no link in Amazon yet)
$80-100 - foot pod (if you want cadence)
Garmin Foot Pod SDM4 (ANT+)
$35-50 - speed/cadence sensor (if you want cadence for the bike)
GARMIN 010-10644-00 Speed/Cadence Sensor
You'll be into it for $575 retail. Garmin, you did us faulty on this one. Some of us are more than willing to spend this kind of cash on a product if it proves to do what it advertises itself to do. We're not asking it to do anything more than carry out as advertised. I realize your fine print saves you from lawsuits, but it doesn't gain you repeat customers. It sends them over to Polar.
[EDIT: I have edited the title of this review to what it presently reads from "Misleading: Not a Triathlete's Watch," because it seems that Garmin has more or less softened their advertizing and merchandising surrounding this watch. I purchased this watch when it initial came out in 2009, and at the time the marketing videos and advert in triathlon magazines cited not one thing with regards to the fact that it doesn't track GPS data in the water, and in fact seemed to lead the buyer into believe it does. That advertizing has since softened.]
Decent watch, but a lot of catches
The 310xt was my primary Garmin purchase. After years of having family use the Edge and the Forerunner for biking/running I decisive I'd take the plunge when they came out with "the triathlete's crucial training tool" in the 310xt.
My introductory thought was this was pricey. But, looking at the ForeRunner 305 & 405, I realized it wasn't that much more costly for the further and added supposed features and the "newness". Then I looked at the price here on Amazon and closely passed out. $550? Without the HRM strap? Ouch. If you're actually into this watch, don't buy at that price. Search for the ones priced at $399. Most internet sites trade at that price.
Ok, onto the feature set. Large, clear buttons. Large screen. Ability to track multiple sports. Quick upload of data. Lots of customizable choices and screens.
Pros:
Easy to set up and use. Pairing with the ANT USB stick is simple and may quickly get you started without the manual.
Online tools are beauteous good (much better than former iterations). Also, works with the MapMy list of internet sites (fitness, run, walk, hike, bike, swim, tri).
Customizable display allows for up to 4 tracking items per screen. So, you may track pace, HR, time and distance covered on one screen then scroll to another and get a map of your HR, your calories burned and a bunch of other potential options, all determined by you.
You may manufacture routes on your watch and when you run it, it will record whenever you are on that route path. Great for comparing versus former training routes and for quickly setting the route and having it track you properly. Once you are on the route, it tracks you.
Auto-multisport option allows you to set that and when you click lap, it will dump you to the next "sport" whether it be a transition or another sport such as biking/running.
Tracks you the person after you enter your height, weight, level of fitness. Provides caloric burn and other related info based on your input.
Virtual training partner. You may actually have it show how you're doing on a saved route versus your virtual training partner. This collaborator is a former version of you doing the same route and tells your pace and how far you're up/behind. Pretty cool.
Multitude of things you may configure and display/adjust/fine tune.
Cons:
Swim? As I cited from the Garmin website above, this watch bills itself as the triathlete's necessary training tool. Umm.. triathlete means 3 sports, distinctively involving SWIMMING, biking and running. Swim is not an option. In fact, when I clicked other one time, it had what appeared to be an icon of a downhill skier. I'm not sure how that showed up since that option isn't there. HUGE fault in my book for a watch billed to be for triathletes.
Elevation Accuracy? This one is WAAAAAY off. On a 3.3 mile run, it had me ascending 853 feet. Unless I'm climbing the Washington Monument, I'm not getting that type of elevation in 3.3 miles. I'd have to say it is off by, 600 feet or so. On a 60 mile bike ride, it had me at 1500 feet and that one at least took me up some lawful hills.
Switching events: There is no way to switch events mid-stream on the watch if you didn't set it in the right manner to begin. Let's say you ran one day and then biked the following day. If you left it on run then swopped when you realized the mistake, it clears the data and you begin with a new workout. The introductory workout is held but you can't append the "new" workout on either on the watch or with any of their software (both installed SW and online site). So, when workouts are categorized, it shows a multisport recording on the installable software and whatsoever you mistakenly set in the online site. You then have 2 workouts you can't consolidate or run reports versus without manual intervention.
Swim accuracy leaves a bit to be desired. While I haven't put it through it is paces and will hopefully edit this review in the future, for a 1/2 mile swim, this thing was way off. Beach, opposite direction, gaps. All were part of that swim result.
While there are a lot of masters (which do warrant a 4 star), the cons are exceedingly negative. Since I don't have a watch to keep track of everything, this one will have to do. At such a price point, I'm highly disappointed in the overall performance giving careful consideration to it is billed as the triathlete's dream. It in truth does track mileage well and with sufficient fudging (using the elevation in MapMyRide rather of from the watch) and by manually adjusting routes in my respective tracking sites, I may get close what I want. The HRM is good and the coupled effect of it all makes it as suitable as having a set of watches out there. But, I will not be at long last encouraging this to other athletes. While I've managed to make it work to a 4-star rating with my own fiddling, I wouldn't commend it to a hardcore triathlete. Being my introductory training watch for my initial Ironman, I wish I could say there were other watches which had the functionality I needed. Unfortunately, I'd have to wear two or more plus a bike computer. Even more unfortunate, in order to get what this watch said it may do all in one I might still need another to keep this one honest.
