I tell them when they join. I remind them when they get issued a new machine. It's in the damned IT Policy which they have to sign a form to acknowledge that they've read. And there's still some idiots that assume they can use work machines for browsing porn. I tell them "Your web usage is logged, and every so often I amuse myself by going through those logs". Ye gods. EEEEEEEEEEEEEEEEEEEEEEEEJITS! *SLAP!*