By now is official Windows 7 will be released between last week of April and second week of May!!
Many sites (http://www.engadget.com, http://www.hwupgrade.it/, http://blogs.msdn.com,…) report these weeks, but for now there isn’t a fixed day because Microsoft doesn’t want repeat the errors of first public beta and it is preparing a more efficient download system.
How will it can download? Microsoft didn’t decided if RC version will be downloadable for all, but for now it’s sure that tester which submitted a number minimum of feedback will can download new version.
Windows 7 RC will stop to work 1 September, only one month after first beta. The reason of this choice is that Microsoft received good feedback and thinks that RC fixed bug of first beta. It might be thought that Microsoft wants anticipate Windows 7 launch at January 2009.
The some changes between Beta and RC are reported on this page: Some Changes Since Beta for the RC.