I think Diaspora and others will fail because it is tackling the problem from the wrong angle.

I don't think people really want to micromanage things like that. Think about it. Every time you post a tweet, picture, blog post etc, do you want to meticulously decide who receives it, or would you rather click "all" and let everyone else decide whether they read/view it? Conceivably all facebook needs to do is tweak how you recieve messages a bit and these startups are toast.

You can't defeat Facebook by adding one little feature Facebook doesn't have. You need to come up with a completely paradigm-shifting approach.