TUAW reports that Mac OS X Lion has been released for "internal testing" last week at Apple. It's not clear what that really means, but TUAW believes that means that Lion is nearly ready for release.
This suggests the new OS might possibly ship as early as WWDC with an "available today" mention at the keynote -- or it might not. But Lion is looking to be one step closer to availability for Apple customers.
We do know the last Mac OS X Lion developer preview was said to be much faster and more stable than the previous releases.