As Todd recently pointed out, if blocks can be made full by the owner of a pool himself spamming transactions and forcing fees up (perhaps losing nothing – in even the worst case scenario – because the fees are paid to himself) he then gets to collect the huge fees that everyone else is forced to pay. The more likely a pool operator is to find the next block, the more incentive he has to perform this attack.

I have not really heard this discussed at all, but perhaps I am just out of the loop.