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.