I was going to do that on my forum, than the idea crossed my mind, that maybe some people register, not because they want to post a message, but because they want to be able to see what messages are new next time they visit.

So when I get around to deleting the dead flesh, I think I'll do a check for post counts and last time they logged on, because obviously most of them are probably failed spam attempts, but some might be my suggestion above.