Preview at WWDC likely in June, followed by September launch.
OS X Lion Not Going to Launch This Week?
Meanwhile, Arstechnica's John Siracusa said during his podcast (within first two minutes) on 5by5.tv that he'd also heard that Lion is not coming this week. Siracusa, however, describes the information as "third-hand, fourth-hand" information.
So while neither source is particularly concrete about their predictions, given the anticipation surrounding OS X Lion's release, we thought it worth noting.
If we do believe that OS X Lion isn't coming this week, then despite the leaked part numbers, it's almost certain the new hardware will also not launch this week. At this stage Apple is expected to launch the new MacBook Airs and Mac Minis with Lion pre-installed, so they can't launch the machines without first officially releasing OS X Lion to the public.
For Apple's part, they have only promised that OS X Lion will ship in July, and have made no promises about new hardware.