Pruning my friends improved my experience, but they grow back over time as people rediscover you or you make new acquaintances. I wonder if you could make a game or website that forced you to prune your facebook friends down, perhaps by looking at your social graph and telling you that you haven't messaged with a person in x years or something, or that you've never even "liked" something they posted. Some heuristics to determine who you really wouldn't miss. The problem with unfriending is that Facebook's UI makes it almost impossible to do in batches, and it feels kind of rude to "unfriend" someone, even though I personally wouldn't care if someone I don't talk to unfriended me.
A game rewarding you for removing Facebook friends? Burger King did that years ago, got quite a bit of exposure thanks to it: sacrifice 10 friends, get a Whopper:
Here's a trick to constantly pruning down your friends list. Don't worry about pruning down your whole list, just check the people who have birthdays every day you log in. I just checked; there was a single friend who had a birthday today, and I haven't had any contact with her in years. That makes for a nice easy prune.
Of course the downsides are that you risk disappointing someone who obsessively checks their friend count on their birthday, and that it only really works if you log in every day.
If you don't care enough to talk them in a year, then I doubt you care about "disappointing someone who obsessively checks their friend count on their birthday"
It isn't really outrageous when you consider their core business model and the value of keeping you in a widespread graph of people. Someone with some time could easily do it with a plugin manipulating the JS on their friends page though.
I did this. One day I just decided to make my Facebook account family only - removed hundreds of "friends". It worked great for me. I don't idly check it so often (because there are fewer updates), but I still get to see what people I care about are up to.
