Stand-alone GPS units may be going away due to the functionality being incorporated into so many other form factors, but that doesn't mean GPS companies are standing still. Garmin for one continues to improve its Forerunner series of wristwatch style units. The 310XT is the latest, upgrading to a waterproof housing.
The 310XT is similar to the Forerunner 305, but slightly smaller because it ditches the wraparound receiver housing. Like the 305 the 310XT acquires satellites quickly, has a good software interface and the display is highly customizable so you can see just what you want. There are various useful quick-release options for mounting on your bike, foot pods, etc. Timing and distance on land are very accurate, as are calorie stats. Some settings out-of-the-box you'll want to change, mostly audible and vibration alerts, although in some circumstances they can be useful.
The 310XT weighs just 2.6oz and is waterproof to 50m, so you can swim with it. Know before you buy that the GPS functionality does not work in the water: you get timing only, not speed and distance, which for known distance training such as in a pool shouldn't be an issue. You can log transition times, and easily switch sport modes between run, bike and other (you read that correctly: no swimming mode). One nifty feature is the wireless two-way data transfer, which works as advertised. You can load programs and goals from your PC to the 310XT, and download training data the other way. It also connects wirelessly to ANT+ enabled devices like footpods, cadence sensors and even digital scales.
The battery life is rated at 20 hours, but like all GPS enabled units using the GPS will lower this considerably. Be sure to power down the unit when not in use. Also be certain to upgrade to the current firmware version to account for various small but annoying bugs. Finally, all you short-cutters out there, you know who you are: RTFM! This is a complex little computing device, and if you're serious about improving training and making this investment you want to get the most out of it. While you're at it, check out the online support forums on the Garmin web site. If you've got the dime and you put in the time, the 310XT will repay.