Equivalent situation here in Australia. Upgraded ATV with latest update as prompted and then ATV won't access itunes. Previews work, network test even works (but not always), but as soon as you try to rent a movie or view your music library it fails to connect to itunes - can't connect to server. Pulling out the ethernet cable it will connect to my network via wifi and all is back to 'normal' and content accessed withouth issue.
I've never used ATV over Wifi (and don't want to) and never had a problem with ethernet until now. It is very clear this is an issue with the latest ATV update. My whole house is wired with Cat 6 so we essentially don't use wifi, except occasionally for iPad. I have up to five macs, plus printers and storage devices using the network at one time at home without issue. Each device on the network has a static IP address, including the ATV, and this has worked perfectly for many months until the update. Its pretty robust for a home network. I now have all devices connecting via ethernet, except the ATV, which connects to the same router via wifi. Nice that its working, but it took a long time to get there and its a workaround I don't want to persist with.
I was just about ready to throw away ATV after two nights of trying to rent a movie, in between times getting an email from itunes confirming my credit card had been charged for the movie, even though I couldn't download it (- a nice touch). Before realising it was an issue with ATV and ethernet i'd been through resetting, restoring, and changing all conceivably relevant settings on ATV and router, only to find a couple of threads tonight about it being an ethernet issue with the update. I can now actually watch the movie tonight, but what an absolutely fundamental stuff up when so many people can't use a device designed for high bandwidth content over their gigabit ethernet LANs and need to rely on wifi (only of course after taking hours to work out they could get it to work that way as a workaround).
I'm one of the true believers Mr Apple, I want to belive and promote, but this is really disappointing. There needs to be better quality assurance on releases like this. We all know its a complex world, but when your brand is built on having stuff that 'just works', it needs to.
Hopefully some lessons in this and we can get good support and a new update and better performance going forward in terms fo quality assurance around updates.
Good luck!