I have the Garmin 305. It took me a year to figure out how to use it with some proficiency, but now I'm in looooooovvvvve.

It is very techie, with a novel for a manual, but check this out...

http://trail.motionbased.com/trail/user/h2odiva

This is the data you can get from the garmin about your workouts. Waaayyyy cooooolll.