There is location and then there is behavior.

Google Latitude, which effectively embodies the business case of Loopt until some kind of conversation occurred at Google, allows users with mobile phones to opt-in to a service which broadcasts their location. People can search for their friends locations and retrieve Twitter-like messages by them. Location is a good start, but more interesting is a presentation I recently viewed on behavior and its use for location based apps like this one. Why just try to find your friends somewhere when you can go ahead and predict where they, and people like them and you, are going to be? I rather like the privacy policy too (anonymity, you own the data you create).