Erica Sadun over at TUAW writes that "trusted sources" have indicated that Mac OS X 10.7. Lion has "gone live for internal Apple testing". Such a move for the next major Mac OS X release is said to point towards a "near to real world debut".
Sadun goes onto speculate—without reason—that this could mean a WWDC debut of Lion. Such a move would be surprising with Apple historically releasing one final developer release based on a Golden Master (GM) at WWDC with a public release following in weeks or months after.
Common sense would say that releasing a major build of Mac OS X to the public whilst thousands of engineers who helped create the software are in San Francisco would be asking for problems.