Yes!
I don't see botnets as an issue, if they become too often there are ways to prevent them for pools (and if they begin using there own pools there could always be changes in the bitcoin client to prevent this).
If one were to set up multiple proxies that for every few proxy IP's there was another account. That may defeat the pool-side detection, but for the ISP, it would probably look suspicious to have tens thousands of small packets going to the same IP every few minutes.