This is the Holy Grail of mobile social networking, and one of the main reasons for taking the networks off the desktop/laptop environment in the first place. Imagine walking into a meeting, classroom, party, bar, subway station, airplane, etc. and seeing profile information about other people in the area, depending on privacy settings. Picture, name, dating status, resume information, etc. The information that is available would be relevant to the setting - quick LinkedIn type information for a business meeting v. Facebook dating status for a bar.

Knowing when your friends are around, and having the ability to meet new people who share your interests (even if it’s just that you are both single), will drive massive usage of networks. But, as with many new services, a chicken and egg problem looms. Until everyone is using this, there is no real reason for anyone to use it. Meetro, an instant messaging service that finds friends based on location, has struggled to gain users over the last couple of years for this reason.

Technical barriers aren’t an issue - cell phone tower triangulation and bluetooth solve a lot of the problems of locating users and transmitting information between phones. What’s harder is just plain getting a critical mass of users.