Apple updated the Web page for this year's World Wide Developer Conference today, making explicit mention that OS X 10.5 Leopard will be shown off for the first time there.

From that description, it sounds like, at best, attendees of WWDC will go home with a Developer Preview edition of the software at the August convention, and we're still many months from the shipping version of Leopard.
(Thanks to AppleInsider for the tip and ComputerBase for the graphic
