There are no Facebook alernatives. My friends and family are on Facebook. They are not on ANYTHING else. Until that changes, which I suspect it won't, nothing else will be viable.
For instance, a lot of people are on niche or community-driven social networking sites, alongside facebook. If those sites could communicate with each other, facebook would lose a lot of mind share.
Don't get me wrong. I'm hopeful for a new world of open protocols and you controlling your own data, but I just don't see it happening right now.
I do think it's an inevitability, and it's really just a matter of how soon it happens. Mark my words though, within at least 5-10 years from now, Facebook will look more like the AOL of social networking.