From here:
https://en.bitcoin.it/wiki/Weaknesses#Denial_of_Service_.28DoS.29_attacksBitcoin has some denial-of-service prevention built-in (it will drop connections to peers that send it too much data too quickly), but is likely still vulnerable to more sophisticated denial-of-service attacks.
Does pushpool have any similar dos prevention techniques built in or is that up to the pool operator to take care of?