When I was watching Andrew Zimmern's Bizzare Food (dozing in and out of sleep). Within my daze, I had the Diablo III box within my grasp, and the date of it's release was December 6th, 2011. You heard it here first!
Bashiok, feel free to confirm said date, :) !
-- I remade the post because I don't want people thinking I edited the date when I am correct.