On Google's new Plus page (plus.google.com) is says "We've temporarily exceeded our capacity. Please try again soon."
I know this is referring to their Google+ "Social Networking site" but this could be affecting the +1 button.
It's still early days for Google Plus, and they've already had to stop people from signing up, even if they've received the invitation email (Like myself).
Tried the +1 button on a few websites, some work, some don't. My personal XF site +1 button isn't working and neither is the one on this site.
Would be great if Plus can be a success for Google, they don't have the best reputation for creating this kind of system, I just hope they can change the view of so many 'haters'.
-Dan.