It will be released May 15th.
I just got off the phone with tech support at battlenet about 90 minutes ago with questions relating to WoW. But I did ask some about D3. It will be STRICTLY regional. So players in Europe and North America will NOT be able to play against eachother like they did in Diablo 2. Also, those in Asia will not be able to play against those in North America or Europe.
I was told it is because of "legality" reasons as well as the fact that "real money" can be used as certain auction houses to buy items. So, basically, it will be like WoW for regions. Even though game play in D3 will be totally FREE except for the real money auction houses and purchase of the game.
IF you are in North America, you should probably be able to play against Latin American, Brazil, Australia & New Zealand, since you can in WoW.