I don't know about you, but I'm a bit sick of reading inappropriate status updates on Facebook, purportedly from my friend or family member, but in actuality from some friend of theirs who found their machine still logged in.
So, I'd like to propose a feature: Confirm My Status (or Yes, I'm Sure I Want To Say That). Since you're no doubt checking what we're posting as we type it anyway, why not monitor for explicit language, and then ask for our password to confirm that we really want to say what was typed. The logic here is that those who have stumbled across their mate's logged in Facebook profile won't know their password, so won't be able to confirm.
Just a thought.