I just stumbled across this blog. Whoever is behind it has both done their homework and has insider connections. He accurately called Pandaria as the setting of the World of Warcraft expansion as early as March, and everything else he's predicted has been dead-on down to specific details (such as the real money D3 auction house, or the Pandaren racial traits).
So basically, the original release date for Diablo III was going to be November 24, 2011, and the backup Q1 2012 date is January 17, 2012. Given that it seems they had already planned for a possible delay, it's likely that they will stick with this release date.