From time to time I receive messages "[username] wrote on your wall". The links are valid links to F.B., but when you go there, no post . . . and if I go to [username]'s page, there are other "friends" asking, "hey, I just received a message about you posting on my wall and see nothing?"
What distinguishes this from normal messages is that usually the wall post content is actually IN the email you receive, in these it is not, which is what raises the first suspicion. The headers are all correct, the links validly go to F.B., and no attachments.
I couldn't find any docs on this, it's a low level issue and doesn't appear malevolent, but wondering if it indicates some glitch in F.B. (big surprise,) a hacked account, or some other new and unrevealed hack.