This is a reminder post for all the Windows 7 users still using the Release Candidate (build 7100) that was released to the public in May 2009. Bi-hourly shutdowns of this build will begin on March 1, 2010.
This means that the user will be told to install a released version of Windows and their PC will shut down automatically every two hours. On June 1, 2010, if you are still on the Windows 7 RC, your license will expire and the non-genuine experience will be triggered. Your wallpaper will be removed and "This copy of Windows is not genuine" will be displayed in the lower right corner of your desktop, above the taskbar. Starting on February 15, 2010, Windows 7 RC should actually start giving daily prompts to remind you about the expiration, but just in case two weeks' notice isn't enough, we're letting you know a month in advance.
If you want to continue using Windows 7, we recommend moving over to the Windows 7 RTM (build 7600) that was released to the public in October 2009. Microsoft explained that this would happen when it gave out free copies of the beta (which has already expired) and RC builds, and you've had plenty of time to move over. If you haven't reinstalled a final copy of Windows, do so as soon as possible so as to avoid problems in the next few weeks.
source: arstechnica.com