Microsoft have accidentally revealed the availability date for the public release candidate (RC) of Windows 7. Showing up on TechNet, the Windows 7 Release Candidate testing program will be available for sign-ups from May 2009 through to at least the end of June 2009, with both 32-bit and 64-bit versions in English German, Japanese, French and Spanish.
The page has since been taken down. What we know, though, thanks to a screen-grab is that downloads will not be limited and Microsoft's product keys will be valid until June 1, 2010.
Minimum specifications are unchanged from the public beta of Windows 7, which means a 1GHz 32-bit or 64-bit processor, 1GB of RAM, 16GB of storage and DirectX 9 compatible graphics (if you want Aero). Originally the Windows 7 RC was expected in April 2009.