I just deleted my Facebook account less than 5 minutes ago because my wife does not know how to properly use it and put too much crap on there. Now I won't see it at least.
But in regards to the OP's question, my Aunt got a hold of my grandmother's password somehow after she died. Lo and behold, everyone started getting these encouraging messages from her on their pages whenever they would post something depressing, upsetting, contemplative, etc. We pretty much knew it was her right away, but due to the sensitive nature of the issue, we waited until we had proof (my cousin caught the account logged in on his mother's computer). It was dealt with, and the account was deleted. It was a really strange incident.
I *had*, until recently (see above), a friend on Facebook from the Army who suddenly died not long after I found him on there. His friends post on the page occasionally and its kinda cool. Once in awhile, his brother, sister and wife post messages about their current events. I actually thought it was a good idea.