This week's routine server maintenance window for US realms has been announced in-game and on the forums. You know the drill! This happens every Tuesday, nothing to see here, certainly nothing to complain about.
Downtime is scheduled to start at 5:00AM PDT/8:00AM EDT and end at approximately 11:00AM PDT/2:00PM EST. This is, of course, assuming no extra maintenance time is tacked on due to issues.
Disclaimer: Patch 3.3 is not coming out today. But, you can certainly read up on the new additions to the game with Patch 3.2 in our Guide to Patch 3.2 if you need to kill some time whilst you wait for your server(s) to come back up.