I have Facebook and have a fair variety of people on it but it's mostly dip in/dip out/here are photos of my trip. Mostly use email/SMS/iMessage if it's arranging a get-together with a closer overall group.

With Facebook, I think it is partly the feed but it's also that I've accumulated a fair number of mostly professional colleagues and friends-of-friends over time. Some classmates I've stayed in various degrees of touch with.