I predict a March 2012 release for Diablo 3. Blizzard has posted this...Also, if you watch the videos they say "Diablo 3 is almost ready" or "We are almost done with Diablo 3"
Diablo 15 Year Anniversary - Game Guide - Diablo III
At the bottom of the page
The Diablo III beta is underway and we’re counting the days until the latest chapter in this storied franchise is ready to be unleashed upon the world.
We look to Diablo’s legacy and the passionate player community for inspiration -- they drive us to make Diablo III the best entry in the series yet.
We hope you’ll enjoy playing it as much as we’ve enjoyed creating it.