Yea, I’d think the best way is to just bust them for not doing the work they should be doing, rather then going after whatever specific time-waster they’ve found on the internet. After all, there’s always ways to dick around and not do work, internet or not. So the problem isn’t really them logging onto Facebook, its their not doing their work.
Plus, adding nanny cams and checking browser histories just makes the new time waster “how can we circumvent this particular way the boss is trying to check up on us” which is often a more fun timewaster then Facebook anyways.