I have just deleted my Facebook account. I cannot remember exactly when I joined, but it was probably 5 or 6 years ago. A while ago I already removed most information about me (such as what music or books I liked), as I felt increasingly uncomfortable with FB's way of making more and more of your information about you available to other people, unless you explicitly disallowed it. This did not feel very honest to me.
And then today came the proverbial straw: I read two (unrelated) posts about FB in direct succession which convinced me that it was finally time to cut the cord. The first , showed how FB does not really 'log you out' when you log out - it keeps certain cookies in place which can identify you. I don't use many public computers (especially not with FB) so this does not overly concern me, but I see this as yet a further violation of default expectable privacy.
The second article was vaguely similar, and shows how FB can track where you have been, and other sites can post on your 'wall' when you simply read a webpage. This is just silly. I'm - again - not overly concerned about this (along the lines that I don't generally do things which are illegal or immoral), but on top of that it just contributes to the already existing information overload. If I need to care that person X read webpage Y then I would expect X to tell me. I don't want a stream of activities swamped with reports what websites people I know have visited.
Anyway, those two articles were enough to sway me far enough to permanently delete my account. Not sure what 'permanently' means in this context. For at least the next 14 days FB keeps my account in case I'll change my mind, and I don't exactly trust it to delete anything for real anyway. Remember, in the FB business model, FB's assets are you, its users and their data, which they mine and sell on to other people.
Will I miss FB? I haven't really used it that much in the first place. I'm much more active on Twitter, which is somewhat less intrusive and has fewer opportunities to do stuff with my data. I won't now not as easily be updated on what some family members who live abroad are doing, but there are other ways of keeping in touch. The main issue is our postgraduate students (I am coordinating our English Language PG students) - they have recently set up a FB page, which I now won't be able to see. But most things are still posted on a traditional mailing-list anyway.
On the positive side, I no longer need to deliberate whether I accept somebody who wants to be my friend or snub them if I only vaguely know them. Fewer decisions to make equals more happiness.
It feels weird, cutting the cord, as it did with any account on any system I spent a reasonable amount of time on, but in the long run I don't think I will shed any tears over it. I'm just concerned that FB will spread its tentacles out further, so that at some point in the future everybody is expected to have a FB account, and you cannot do certain things without one. Matrix, anyone?
 Apologies for the shortened (and thus opaque) links - they're directly copied from the corresponding tweets