Josep just sent me to a link to a great article on MobileMarketer. It talks about a free BlackBerry application that combines social networking with your location. Personally I think I have to try it to understand what that means but here is my best shot.
Essentially it lets you rate your current location and share that rating with your friends. That way they can know what you like and if they should come or stay away. It also lets you share your location with your friends along with tracking your location. Not exactly sure how they do all these things but hopefully I will be able to tell you tomorrow afternoon once I have some time to try it out.