I use one on the treadmill. When I calibrated it outside, I used my Garmin Forerunner 305 at the same time and it seemed very accurate (matching the reviews I've read). IMHO, carrying an ipod seems a whole lot more cumbersome than the newer GPS watches.
I'm also not sure how robust the custom workout creation functionality is. Nor am I impressed with the nikerunning site. It's mostly pretty marketing graphics.
The absolutely minimal approach is the Nike Sportband.
Frends know gud humors when dey is hear it. ~ Da Crockydiles of ZZE.