i bring my phone, but don't use it for data because (1) i find the GPS to be inconsistent (it uses aGPS, not straight GPS like a garmin) and (2) draining phone battery isn't great when you're far from home
that said, i WISH i could just bring the phone. to have my camera, video camera, ipod, gps, and cycloputer in one device would be wonderful.
but the battery tech isn't there.