I have the Timex Bodylink system. I really like it actually. Very easy to use --took me about 15 minutes to get it set up and figure out how to use it. The only issue I can see for tri's is that it takes a few minutes to lock onto the GPS signal at the beginning of your run -- but I guess you could just turn it on when you're setting up your transition stuff before the race and leave it there, on, and put it on either in T1 or T2 (you don't really need the GPS on your bike b/c of the computer, and since the unit is separate from the watch, it might be easier just to use it for the run).

I've found that the real-time pacing is pretty accurate.

The newest version does measure altitude/ascent & descent rates, so while you don't get the fancy readout on the watch itself that you seem to get with a Garmin, if you get the data recorder, that is recorded and can be uploaded and graphed, etc.

I have tiny wrists and while the Garmin seems really cool, I don't think I could wear it.