Today is Blizzard's shareholder conference call, and they will be required to tell the shareholders if they are going to push it back past Q1 2012.
There was an interesting write-up at one of the Diablo Fan sites that looked at the habit of Blizzard in announcing their products release date at least 8 weeks before release. It turns out that Blizzard has announced every product they have released since WoW at least 8 weeks early, which makes since for marketing reasons.
So, if they do say today that they still intend a Q1 2012 release, that would mean that if they intend to release in January, they should announce the release date in the next week or two, if they do not we can probably expect a February release, and will know about it early December.