I find it useful for finding people you haven't seen in years, to organise events, to get group assignments done, and to contact friends and such, but I find it too public. You can comment on practically anything you do, from talking to someone else, to posting a video, which I don't like.
It's also filled with pointless crap that just wastes everyone's time, pointless threads and stupid groups. Me and my friends in University have nicknamed it 'Failbook' because people are more likely to fail when they have assignments due and are too busy chatting on Facebook. I know people who just don't really log off, and check the site like five or six times a day, possibly more.
