I can see it now, photos like in the photo browser, showing the profile pictures of all the horny N900-owners who are nearby. You could then click someone to view their profile, and if satisfied, proceed to initiate contact via IM.

Considering that this is not exactly a very popular device, and I'd say less than 1% of the userbase would use an application like this, you're likely better off using Facebook...quite specific, I have to admit, wanting to have sex specifically with people who use a N900.