"While most people who tested Windows 7 have now moved to the final version, some are still running the Release Candidate. If you haven’t moved yet, it’s time to replace the RC.
Starting on March 1, 2010 your PC will begin shutting down every two hours. Your work will not be saved during the shutdown.
The Windows 7 RC will fully expire on June 1, 2010. Your PC running the Windows 7 RC will continue shutting down every two hours and your files won’t be saved during shutdown. In addition, your wallpaper will change to a solid black background with a persistent message on your desktop. You’ll also get periodic notifications that Windows isn’t genuine. That means your PC may no longer be able to obtain optional updates or downloads requiring genuine Windows validation."
What's funny about this is that as far as I can see, continuing to run the release candidate after March 1 is different from using the final version (which I've been running for a few months now) in just 2 ways:
#1 the live version shuts down about every 8 hours, instead of 2 hours
#2 it shuts down with a blue screen rather than a black one.