To be honest, I actually created a Facebook account back in 2009 ... but I knew full well what Facebook was about so I felt dirty and requested it to be deleted closely after.
I never used it for anything, never used it to find any groups or people, etc. The only info they have on me should be the data I supplied on registration, and of course from tracking my IP address through buttons on other web sites for a short while.
I have all (or most) Facebook domains blocked in Privacy Badger.