Facebook taking control of the world is not really that bad. It's only uncomfortable.
It's similar to the Microsoft empire from a few years back. Windows knew everything about you and you were completely locked-in not being able to stop using it because you had all your apps there.
Now you have all your friends there.
From application developer point of view this is actually a good thing - you have a common platform to code for. And it triggers innovation as we don't have to reinvent the wheel - there is the default social network already, so let's build on top of it!
Of course it would be great to have a free, distributed, open source social network anyone would join and leave at any time (think: Diaspora). Just as it would have been so much better if it was Linux or BSD who gained the monopoly on desktops, not Windows.
But we survived then and we'll survive now.
And if Facebook starts being RELALY nasty, people will finally leave it for something more friendly, cooler or maybe just new.