Diablo III was mentioned breifly in Blizzard’s portion of the Activision conference call this afternoon. And the developer hasn’t committed firmly to a release date. From what it sounded like in the call, the game will not be releasing in 2011. Which was quickly pointed out to Game Informer that was false. So the official news is that the company does not know, or has not decided on a firm release date for the title. But judging from the context that the conference call had, it is not to be expected in 2012.
What was said is the call was that Blizzard did not anticipate releasing a game made by themselves in 2011. Which would be Diablo III. If this does turn out to be the case, 2012 will be a banner year much like 2010 was for the developer. Housing both a Starcraft II release, and a possible Diablo III release.
Source: Activision Conference Call & Game Informer