Today isn't a good day to stay home playing Diablo III, according to Battle.Net. Blizzard has taken down the Diablo III servers in the US today, preparing to integrate the game's next patch, version 1.0.3.
Blizzard took the servers down at 3am Pacific, in case you've been trying. The game will be back online and ready to go at about 1pm Pacific, almost three hours from the time of this posting.
Before you say it's unfair that Blizzard only turned the game off in the US, you should know that the European and Asian servers will be taken down for maintenance tomorrow.