The Associated Press has a review of the Garmin Forerunner 201 (pictured to right) and the Timex’s Bodylink System (pictured below), both wrist mounted GPS units for runners. Each unit has specialized functions for specifically for runners.
For example, the Garmin allows you to run with a virtual runner on the display who runs at your specified pace. One could imagine Garmin or Timex building future units to allow Olympic runners to against AI virtual rivals to better their game based on their performance.
The AP article says the timex tranciever is superior in GPS performance, but the Garmin comes with the ability to transfer data out of the box, and records elevation and incline information. While Timex is silly to not include something so basic as altitude, unlike the Garmin, you may have to purchase an add-on to get a heart rate monitor for $36. The Garmin comes with the ability to save running data, and software to make graphs of your performance, while the Timex needs an add-on (which comes with the data cables), for $50.
Another feature the Garmin has that the Timex doesn't software to encourage you to try new trails while giving you directions to get back, which sounds really neat to me, but the reporter says that on average the Garmin took longer to get a satellite lock, and also lost it's signal more often, especially around tall buildings.
Garmin Forerunner 201: $130,
2.8 ounces, better for rural areas, better features.
Timex’s Bodylink System (with heart rate monitor): $232
~6 ounces, better for citites, expect to pay $282 to record data.