I don't have an iPod, so I'm just passing this on for those that do. As many of you know, Nike has released an iPod enhancement that fits in Nike shoes, the Nike+iPod Sports Kit. As far as I can tell, this only fits in one model of Nike shoes. So if you don't wear that model (I think they are hard to find right now) or if you don't wear Nikes at all, this guy (the Podophile) has found a good solution.
It looks to me like this is a fancy pedometer; I've never trusted pedometers. If I ever want to know my distance, speed and pace, I use my Garmin Forerunner 201 (although the 205 looks pretty tempting).