Apple has filed an interesting patent which describes a mobile phone application that allows groups of people to share information about a live event as it's occurring. It's called iGroups.
It ties in with MobileMe and uses a very sophisticated cryptographic key generation system to make sure that your data stays private among the people you want to share it with. The patent also adds that if your handset lacks GPS capabilities, it can use MobileMe to provide virtual GPS capabilities - presumably depending on your IP address.
What's more, the app could automatically build groups of people based on who's in close proximity to each other at any time - your crowded commuter train could suddenly get its own chatroom, based on Bluetooth. You'd be able to opt-out of such situations too, however.
It's an interesting idea, but one that presumably relies on vast numbers of people owning Apple's gadgets, or the company building apps for other platforms. Somehow we can't see Cupertino rushing to build an Android app, especially after recent lawsuits...