I would love to see an App that would read what cell tower the phone is using, and allow you to set events reference that cell tower.

This would allow you to maybe have the phone go to vibrate when you are in one spot. Possibly an alarm when you reach a spot (nice for a commute on a train/subway).

Don't know if this is a possibility, but with apps like Navizon being able to use GPSish positioning, would be surprised if it couldn't be done.