Maintenance has concluded, and Diablo III is now back online and available for play in the Americas. We're continuing to monitor the service closely and will be sure to alert you if any additional downtime is required. (At the moment, though, everything appears to be resolved.)
For those of you unable to access the auction house, this is pretty standard after maintenance/downtime for Diablo III. To help reduce load and improve the overall stability of the auction house system, the game may temporarily limit traffic to the auction house during peak gaming hours. This is done automatically, and players may occasionally see a grayed-out auction house button as a result. If the auction house button is grayed-out, please wait a few minutes and then try again.
In order to resolve some ongoing performance issues which have persisted after today's scheduled downtime, we have brought Diablo III offline again for urgent maintenance. The issues we encountered are relatively minor, but do require additional downtime to address completely.
We currently anticipate that all services will be back up and available in the Americas after 5:00 pm PST. Should this schedule change at all before then, we'll be sure to provide an update in this thread. You can also follow @BlizzardCS on Twitter for information and updates regarding any of our online services.