The official Windows 7 Release Candidate (RC) is now available from both the Windows download site and Microsoft TechNet. Several bloggers have reported intermittent problems with the download servers, but they seem to be working now.
The RC will be available for download through July 2009 and there is no limit to the number of downloads. You can continue to run it until next March, when it will start shutting down every few hours (the official expiration date is June 2010).
The much-discussed XP Mode will be also available for download starting today. This is a beta version of the Window Virtual PC utility for applications that won't run in Windows 7. With earlier builds of Windows 7, I've had some trouble with VPN clients and mobile broadband cards, but otherwise I haven't run into many issues with compatibility or reliability using Windows 7 betas.