Since the European version of Age of Conan updates ahead of the US, they have already patched and their servers are back online... well, sort of. It turns out that today's patch has caused some server instability, leading to constant crashing and disconnects. In order to prevent this from being introduced to the US servers, the patch downtime has been postponed. It is unknown at the moment when the downtime will be able to go ahead.
Update: The US servers will come down at 9AM EDT.