TechCrunch blogger Michael Arrington posted a solid analysis of the mobile social networking market. He said that all of the big players, while having unique features here and there, lack an essential component: physical presence detection.

"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," Arrington said. "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. 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."

The main problem, he said, is that until lots of users join a particular network and use this exact feature (assuming it were available), there's no reason to use it at all. In other words, it's the classic chicken-and-egg problem.

Check out his article for a rundown of some promising new companies working with presence detection in varying degrees--including one service that sends a quick vibration to your phone whenever you're physically nearby someone else on the network.

The Holy Grail For Mobile Social Networks [TechCrunch]