As many Steam users have noticed, the service has been unavailable all day and complaining in the Steam forums isnt possible, as those are down as well. The reason for this downtime is that the Seattle area was hit by a storm last night, taking out power. According to the Seattle Times story, it could take until midnight tomorrow before power is restored everywhere. With Steam unavailable, people are unable to play games they purchased over Valve's content delivery platform, which certainly shows one of the downsides to a service like this. Update: the forums are now slowly loading, and have this message.

There is currently a wide spread power outage in Bellevue/Seattle impacting Steam Server availability. Unfortunately ETA for when the power will be restored is unknown as the power company will only work on restoring it once the storm has eased and the high winds have died down. Any issues you are experiencing with connecting to Steam are only temporary, as this isn't an end-user issue.