From the Windows Team Blog:
On February 15th, people still running the Windows 7 Release Candidate (RC) will receive a notification reminding them that starting March 1st, 2010, their PC will begin experiencing bi-hourly shutdowns. These shutdowns will continue through June 1st, 2010.
On June 1st, 2010, a non-genuine experience is triggered where your wallpaper is removed and “This copy of Windows is not genuine” will be displayed in the lower right corner above the taskbar. This means your PC will no longer be able to obtain optional updates or downloads that require genuine Windows validation.
To avoid any data loss, I suggest making plans to move to a released version of Windows 7 before the automatic shutdowns start. During these shutdowns, your work will not be saved.
Remember, pre-release versions of Windows are unsupported. For more information on the expiration of the Windows 7 RC, see this KB article.
To move to a released version of Windows 7, you’ll need to do a custom (clean) install to replace the installation of the Windows 7 RC. I suggest checking out this Help & How-To page on Windows.com which covers all kinds of installation scenarios.
Do you need more time to test your application and hardware compatibility in Windows 7? If so, the Windows 7 Enterprise 90-day Trial provides a great opportunity for IT Pros to finish critical testing with a full version of Windows 7 Enterprise.
If you’re an IT Pro ready to move to Windows 7, I suggest visiting the Springboard Series on TechNet which provides the latest tools, whitepapers, walkthroughs and tips and tricks to help you with your Windows 7 Deployment. On the Springboard Series on TechNet, you’ll find resources such as Deploying Windows 7 from A to Z and Installing Windows 7 on an Existing XP PC. You can visit the Window 7 TechNet Forum for more information as well!