If you have bought Diablo III and have experienced lots of downtime since the game's Battle.net servers were turned on less than 24 hours ago, you are most definitely not alone. The players of the action-RPG sequel from Blizzard have experienced lots of downtime from Blizzard's Battle.net servers as the development team tries to fix a number of issues that have cropped up since the launch earlier this morning.
The Battle.net forums tell the main tale. Blizzard has been performing "emergency maintenance" on the Battle.net servers in the Americas for a large fraction of the day. There's already been a few hours of downtime for the servers as Blizzard tries to fix "several issues that are impacting the game".
One big bug that has affected a few people is "Error 3006". As described on the official Diablo III forums, this happens when you give the Templar NPC, found in the Cathedral part of the game, a shield. In short, don't do it. Players have found that when this action happens, they are booted from the game and cannot sign back in.
Hopefully, Blizzard will fix this problems quickly. We will also point out that a lot of these issues may not have happened if Blizzard had not insisted on making people sign onto Battle.net to play Diablo III, even when playing the game in single player mode.