I've also been having terribly horrible quality Netflix, mainly during peak hours. Youtube is also horribly slow to load videos (like 30 minutes for a 5 minute video).
The only way to get HD from either is to run my AppleTV through my Mac Mini's VPN connection.
I use waterroof to create an NAT interface forwarding rule that sends any traffic to the mini through the VPN interface. Then, the AppleTV router address is manually set to the ip address of the mini.
Through the VPN, I can get SuperHD no problem and youtube videos load lickity split. When I switch back to my regular connection, Netflix and Youtube are horrid once again.
It makes no sense. All of my other Netflix/Youtube connected devices are fine through my standard connection, and the AppleTV is fine taking whatever route to Netflix my VPN is using.
It's almost like there's a piece of broken equipment out there in the bowels of the internet that ditches AppleTV traffic and we're all unlucky enough to get sent through it.