Please don't use sequential IDs for this.

I went to the "Track Me" link and got a tracking id of 54. I was then able to look through plenty of other peoples locations for IDs less than 54. I'd suggest switching to something that's much harder to guess.

With that harshness out of the way (sorry :)), it does seem like a pretty cool little app. I could see myself using it for a long road-trip or something so that others could track my progress.