For Windows 7 Beta 1 (build 7100), bi-hourly shutdowns will begin July 1st, 2009. You will be alerted to install a released version of Windows and your PC will shut down automatically every 2 hours. On August 1st, 2009 if you are still on the Windows 7 Beta your license for the Windows 7 Beta will expire and the 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.
Source: Windows Team Blog
