I totally agree that FB gets worse the more you use it and the more it evolves as well.
People hate it. It makes them miserable. But I think it would be a mistake to think that that means it's going down. The social pressures that get you into FB and keep you on it (and keep you from unfriending those people you desperately don't want to see) can be quite strong. Obviously, some people stay off it, or get off and stay off, but if you're married with kids and relatives, and Mom demands you use FaceBook to communicate, a lot of people are going to find it hard to stay off.
It's a bit like a crab bucket, really. You try to escape and the other angry crabs drag you back down. Or even reach entirely out of the bucket and pull you in.
If anything puts a dent in them it may be the unmarried with no kids people who rightly think it's a dull, boring, sanitized padded room and have no interest in it. But once they get dull and boring too, FB will be there waiting.