(Please see UPDATE at end)
I have just permanently deleted my Facebook account. It is very difficult to find out how to do this, but I have finally managed it. Apparently my data will be retained for two weeks, in case I change my mind, but I think this most unlikely. I am currently in process of removing all references to my former Facebook account in my other websites and blogs.
On one previous occasion I 'deactivated' my Facebook account, because at that time it seemed impossible to delete it, but was persuaded back for various reasons, but those reasons have disappeared. I continue to use Twitter, which I find a much more congenial and less obtrusive platform.
UPDATE (Tuesday 7FEB2012 08.02 GMT) I have resurrected my Facebook account, but will be restricting severely the way I use it from now on; I will not (at least for the present) be adding back the link to it here. Apart from a few specific uses (to exchange information with one or two people only), the only motivation for me to return is to retain the username and not allow it to be used by someone else in the future - I'm afraid I cannot write anything more positive.