[psiphi]

I think you mean Navizon... Using Cell Towers only will usually get you within a mile or so of your location. Using Wi-Fi (in a City) will usually get you within 5oo ft, but access points can move, espically between semesters at schools... GPS is the only way to be sure of accurate results, as it will eith give a good position within 3 to 3o ft, or none at all...

I find Navizon good in a pinch (especially in a city where GPS doesn't always work), but would not trust it for every day usage without GPS...

All that said, I usually collect data for them whenever I go biking, as I can track my wife can track me online if I'm needed at the same time...