Well, I know the Windows installation at the end of its testing, will start to shut down every couple of hours ( least thats what I've heard):
*EDIT*
From Windows:
The RC will expire on June 1, 2010. Starting on March 1, 2010, your PC will begin shutting down every two hours. Windows will notify you two weeks before the bi-hourly shutdowns start. To avoid interruption, you'll need to rebuild your test machine using a valid version of Windows before the software expires. You'll need to rebuild your test PC to replace the OS and reinstall all your programs and data.