CF does it on a large scale (many servers around world) and I am pretty sure they have much, much more bandwidth and faster hw to fend off majority of attacks easily. On the other side is saidit - I think they have some cheap hosting/server, so you can't really expect to build their own infrastructure which isn't cheap at all (I am not that knowledgeable, but my guess would be few servers, some heavy duty switches/routers and tons of manhours to make it work, and then someone would have to watch over it constantly).