Actually Google isn't reachable on IPv6 via anon-amsterdam.freenet6.net now. http://www.gogo6.com/forum/topics/google-not-reachable
If you are trying to access Google's IPv6 addresses using the recommendations in here and it doesn't work, then you may be using anon-amsterdam.freenet6.net.
Replying to this old discussion since it is featured on the main forum page.
Why wouldn't it be available via anon on any server? Either you have an IPv6 address or you don't. Anonymous shouldn't make any difference. There may, however, be a routing issue, which would affect all users. That is what appears to be the case with the original post in that other thread.