I found one solution, I think:
When I tried activating the PBS channel using my PC, I had the same issue as everyone else here: I typed in the activation code and couldn't proceed. Instead, I tried to activate the PBS page through my iPhone (using my phone I went to pbs.org/activate, and typed in the activation code that showed up on my Apple TV 2) it worked. You will need to either sign in using Facebook, Google (Gmail) or a PBS account. I would suspect if it worked with my iPhone, it'll possibly also work on iPods, iPads, and maybe just through a Safari browser in general? I'm not sure about any of those, but it's worth a try.