Mine would be the Like button and the privacy features.
The Like button would be for the times I want to show my appreciation to a contact for sharing something interesting on their page, but can't quite think of a comment to write.
As for the privacy features, I have lists (e.g. Fellow dog lovers) so that I restrict my dog-related posts to just the contacts who like dogs too. Sometimes when I don't have much time to spare I get an information overload scrolling through my news feed to get to what I really want to read, so I don't like to spam other people's news feeds either.