There's been a steady series of alternate Facebooks, and none of them have put it all together, nor do most of them deserve the support and optimism of users, of which there appears to be enough to get something off the ground.
In my humble opinion to make a social network worth supporting by idealistic users it must:
Be possible for anyone to run a server.
Accept content authored externally.
Not lock users in.
Be easy to set up and use.
Be fun and interesting.
Not have limits to expression.
Not try to replace existing social networks.
These are just some ideas off the top of my head.
Note there's no mention of advertising. Because there's no lock-in, there can be presentation environments that have ads, and those that don't. All permutations are possible.
Also, it's very difficult to guarantee no ads. What happens when users start posting ads? What do you do then? Is it still ad-free? (I think not.)
I am doing my part, making tools that are gathered around a set of open standards, RSS, OPML and River.js. I'm not the only one. As soon as what we're doing gets easy enough, and the users are willing to accept the tradeoffs of using a non-corporate-owned network (there are some, but also great advantages to balance them), then we will reach liftoff. Will it be Facebook? No. I like Facebook. I want to build off its ubiquity and their great servers. Trying to wall something off and pretend Facebook doesn't exist is emphatically not my strategy.
The title of this piece is a bit misleading, I realize after finishing writing it.