I voted "I used to, but I deleted it.", but actually I have a personal account with no details and no friends, which I only log into on the rare occasions I need to edit a company facebook page, and the login details to a friend's account, for when I want to check up on how Facebook works for the sake of a marketing campaign.

edit: I deleted my account three years ago because it annoyed me and I rarely found myself using it. If that wasn't the case, I'm not sure if by now I would have decided to delete it for other reasons (e.g. privacy) - I haven't really stopped to think about it.