I noticed when you first launch WoW, before going to the login screen, that it says "Gates of Ahn'Qiraj Opened" on the realm of Medivh. Perhaps this programming in conjunction with patch day has caused one too many problems. Dunno, just an idea.
Although, for those that stroll through the forums, I did find this tidbit:
"We are in the process of working with our network provider to identify and resolve the issues surrounding the realms at this time".
It's possible that the servers are fine, but there might be a networking issue that just occurred unexpectedly (bad timing). I know something similar happened once with EQ where they had an unexpected power outage (again, bad timing).