I've got automirror working on my CentOS 5.x machines. I can't say I'm a real expert with it, but if you post your symptoms maybe I can help you troubleshoot it.
Thanks but I've already been chatting with the author who is stumped at this point - so I'm just going to give up.
He said he has found cases where automirror does not work and so he uses polipo in those cases - so that is where I am off to now :-0
I have it working but there is this matter of yum choosing different mirrors ...