Here's my take on concept #1.

Suppose I spend the evening ten-pin bowling with a bunch of friends. Actually, some of them are even "friends of friends".

The next morning I fire up my Maemo music player, and there's a new playlist which says "by the way, most of the people you were with yesterday have been playing these three songs a lot recently, wanna hear them now?".

That would be great! It's better than music suggestions based on a social network that I must maintain online. This one dynamically adapts to whoever I'm spending my time with!

Regards,
Roger