RC is on track for April 30th for download by MSDN and TechNet subscribers. Broader, public availability will begin on May 5th.
Here are some of the changes since beta http://blogs.msdn.com/e7/archive/2009/02/26/some-changes-since-beta.aspx
as well as here http://blogs.msdn.com/e7/archive/2009/03/13/a-few-more-changes-from-beta-to-rc.aspx
I have been VERY PLEASED with the performance and stability of Windows7… I am sooo looking forward to the RC candidate!