They don't let you do simple things ... you can't search your posts, you can't search your inbox (used to be able to, but it never worked right, and now they've taken it away) ... hitting enter submits your comment so to make a paragraph you have to hold down shift when you hit enter (wtf?) ... sometimes links open in new tabs, sometimes they don't so if you're scrolling through your news feed and get to, say, 2 days ago, then you click a link which doesn't open in a new page ... you lose your place and have to scroll through 2 days worth of posts again ...

Little inanities like that.