Today's maintenance period has just been extended an extra two hours according to Datth, one of Blizzard's Tech Support posters. He specifies that the reason for the extension is unrelated to the Battle.net login server 'issue' that's being discussed heavily on the forums. What the reason for the extension is, we don't really know, but I think we all expected it.
The extension does probably mean that those Battle.net users that had concerns over the login server not being ready for them are unwarranted. From what I understand, the work on the login servers is done independently of the patch being applied to the game realms, so the extended maintenance buys the login server folk some extra time. In this particular case, it's a good thing for us, so the login server isn't taunting us while the realms are up.
We'll try to keep you all posted as much as possible throughout the day. Whether the servers start coming up eary or get extended even further, we'll be on top of it as much as we can be.