Preview at WWDC likely in June, followed by September launch.
WWDC 2011 Sells Out in Under 12 Hours
Less than 12 hours after passes went on sale, Apple's Worldwide Developers Conference set for June 6th-10th has already sold out.
Last year's edition sold out in eight days, and brisk sales were expected again this year, but a complete sellout within a matter of hours may still have taken some developers planning on attending by surprise. This year marks the fourth straight year that WWDC has sold out.