I've noticed that a few networks are starting to elicit otherwise implicit relationship data to build out the edges of their social graph. Specifically, Facebook, Yammer, and Path all now ask you with whom you work, hang out, and do things:

This kind of data will prove invaluable for determining the relative strength of ties, measuring interactions between people, and delivery relevant content between friends, co-workers, and acquaintances.

I definitely think they're on to something big here.