I quit Facebook (and deleted my account) several weeks ago - right after the stuff about their shadow profiles came out.
It sucks because Facebook can have its uses - it's definitely a much easier way to keep in contact with some of my friends and family that live across the US and in Europe. But, in the end, what Facebook is doing to its users just is too high a price for me to willingly pay.
What's interesting is it's been obvious for a while that Facebook is trending downward - it's the older folks (my peers) that are really keeping it going. Younger people (e.g. my daughter) mostly still have Facebook profiles, but it's no longer their primary sharing tool. Some have moved to Tumblr, some to other networks - but the tide turned a year or two ago. I'm sure Zuckerberg knew this when he was figuring out the optimal time to launch the IPO, and I'm sure it's why they're pushing harder and harder now. It's only a matter of time before they join MySpace.