I just visited help.ubuntu.com and got a 503 response:
Surge protection Warning: You triggered the wiki's surge protection by doing too many requests in a short time. Please make a short break reading the stuff you already got. When you restart doing requests AFTER that, slow down or you might get locked out for a longer time!
For folks with a shared external IP (which is a lot of freaking people!) this is really problematic. There has got to be a better way to do this.