Kinda straying off topic, but
Kinda straying off topic, but I have had a Garmin 305 for couple years and this spring got an iPhone. I'd read the iPhone was not as accurate as the Garmin, but from my limited sample of several months I find they usually correlate within a few yards each mile. The longer the run the better the correlation. GPS is a rough estimate anyway.
I've stopped wearing the Garmin since I carry the phone with me anyway, plus the iSmoothRun app pauses when I stop, measures cadence, and posts directly to DailyMile. I've tried several running apps and they all have strengths. I use iSmoothRun because of the cadence measurement. I'm up to about 80-85 (ie 160-170, the app reports in 1/2 measurements for some reason).
I'm not ready to sell my Garmin as I think it would be better for long runs. A 1.5hr run drains about 30-40% of the iPhone battery, more if you are streaming radio. I'm an NPR news junkie so I love being able to stream radio while running!
~David