Many people are seeing problems when they try to log into the game or are getting stuck at the loading screen. Others are having authentication issues. Bashiok tweeted:
As Bashiok points out, this is likely due to the new Scroll of Resurrection program. Most of these outages normally resolve themselves in a few hours, so sit tight, read the day's blue posts, and all will be well soon enough.
There are pictures of cats after the break if you really need something more.