Test Realms Up, Live Realms Down

We know that Blizzard is upgrading their authentication hardware today (which seems to be running a bit late, though there's no official word on status), but I am a little confused as to how the test realms are up and all the live realms not. Login to the live realms is painless, but there's not a single realm showing as available to play on. The test realms all appear to be up (as of the time of this writing), but with a bit of a queue and massive crowding in the Eastern Plaguelands as everyone heads in for a glimpse of Naxxramas. However, the fact that login is possible seems to suggest that the delay we're experiencing isn't caused by authentication problems...