Multisport GPS?
 

I'm interested in getting a GPS for training for both running and cycling. Does anyone do this? Which do you think would work better, a Garmin Forerunner 305 (wristwatch) mounted on my handlebars when cycling, or a Garmin Edge 305 cyclometer carried in an iPod-style armband when running. (There would seem to be a market opportunity here since neither one is waterproof like my Polar HRM.)

I use a Garmin Forerunner 305 and got a cadence sensor so in the event of a satellite problem you can still track your speed. It is the best and most comfortable bike/run GPS device.

I have both and if I had to choose one, I would definitely pick the Forerunner.

The combination of an Edge 305 and a Forerunner 50 watch with foot pod works very well for me. They both track my HR from the same strap. I don't run far enough to need GPS and I like the compact size of the 50.