Thinking about it. Not on my primary pc though. Downloads for free and expires June 1, 2010. But you're right. You are on your own, no support what so ever. They are using you to find out their bugs.
If you don't know about Windows 7 (the next latest and greatest due out ???) go here:
http://www.microsoft.com/windows/windows-7/
If you are interesting in being a Windows 7 Release Candidate go here:
http://www.microsoft.com/windows/windows-7/download.aspx