A great idea was just shared here at the Avaya Tech on Tap Event at
ITEXPO East 2012 in Miami. Imagine an app which notifies you if someone you met is within bluetooth range. This could be very helpful for a salesperson at an event like ITEXPO for example.
It would also be useful at a retail store - a gym, department store, restaurant, etc. Lots of possibilities and like with just about everything else - privacy issues.
Take it to the next level - this could be hooked in with Chemistry.com or eHarmony so if a compatible person is nearby you can both be notified. Services like this have been in place in Asia (sans bluetooth) where the carriers are on the leading edge.
Credit goes to Nick Jensen at Dialogic who shared this info with me years ago.