“So..what are the dates?”
Here are the details from the Windows 7 FAQ:
“To avoid interruption, you’ll need to rebuild your test machine using a valid version of Windows before the software expires. Windows will notify you that the expiration process is beginning and two weeks later your PC will begin shutting down every two hours. The Beta expires on August 1, 2009, and bi-hourly shutdowns will begin July 1, 2009. The RC will expire June 1, 2010, and the bi-hourly shutdowns will begin on March 1, 2010. In both cases, you’ll need to rebuild your test PC to replace the OS and reinstall all your programs and data.”
So if you’re running the Windows 7 Beta, you will start seeing expiration notifications in Mid June. For the Windows 7 RC (build 7100) you will start seeing notifications about the expiration in February. The beta will cease to function on August 1, 2009, and the RC will die on June 1, 2010.