If someone's pushing it down he's doing a lousy job, hashrate is going up slowly. We're reaching the gigahash now, which for me makes solo-mining a sad business...
ps. most pools have separate front-ends, which can be DDoSed, but back-ends tend to be more resilient...
Pretty much this. Well, in fact 99% of the pools out there can have their stratum DDoS'd too. Most good pools have real DDoS protection and stratum protection, etc.