Hmm, that Nokia Instant Community does look quite cool. I'm not sure I'd ever use it mind you, but I like the idea.

I don't see why one couldn't implement an app like this to use both ad-hoc wifi and also Bluetooth (to not limit yourself to high-end phones). You'd certainly need to write some Symbian clients for it to get a critical mass (though it would be quite useful for Maemo/Meego conferences as is).