I just quickly said this in chat, only two people were active and one person had the error, one person did not. I also tried it via hidemyass and it works fine, so I have no idea what is going wrong.
For me, going to
http://www.superuser.com redirects to
http://www.superuser.com/error?aspxerrorpath=/ and a generic asp.net error page of
Server Error in '/' Application.
http://superuser.com works fine.
I have just tried
http://www.stackoverflow.com and it redirects without the www just fine.
I have not seen any maintenance banners and as it doesn't seem to be for everyone, I just thought I should bring this to TPTB in case of some error.
Edit, same result on ServerFault pages.