Although there has been much speculation that the Windows 7 Release Candidate will finally arrive in April for testing, it would appear that actually it won't be until a month after that. Who says so? Microsoft, that's who.
According to a page published at TechNet, albeit briefly, Microsoft will be making the Windows 7 RC available for download in May with an expiration date of 1st June 2010. The page, hastily removed by Microsoft, was titled "Windows 7 Release Candidate" carried a publication date of May 2008 and included full download instructions. The page stated that the RC download would be available "at least" through June 2009.
A screen shot of the page can be found here.
Of course, some people are using Windows 7 RC code already courtesy of BitTorrent.