Check this out.. http://www.world-tracker.com/
Tried it with my mobile, and located me to within about 100m.
A few uses i thought...
1. A cheap tracker for your car.. hide a cheap mobile phone within your car. When it gets nicked, you should be able get a rough location for it.
2. Don't trust your wife/husband..... I'll let you lot work the rest out....
Could work against you as well.