Emphatically agree on the utility of a "Spam" checkbox. IMHO:

Nodes up for consideration as Spam should allow $reputation == 0 to be reaped. Nodes lose this special consideration as soon as any Keep/Edit votes are cast. I doubt this special case would be abused intentionally, and highly doubt it would be abused even accidentally by 5/5 monks with consideration power. And, if that ever happened, we'd have a genuine PerlMonks conspiracy on our hands, which would no doubt be entertaining.

Reaped "Spam" nodes should go away quickly and quietly, and (perhaps after a 1-2 day grace period) require deliberate effort to find (such as an Include spam? checkbox in Super Search, available to registered users only). Also a huge ++ to the sentiment that unapproved Anonymonk nodes should never be spidered.