Update: Microsoft have confirmed the shut downs will commence on July 1st and not June 1st as stated in the reminder emails.
Now that we're all waiting for the final version of Windows 7 to be released later this year, there are some important dates to remember if you're still using Windows 7 Beta 1. If you downloaded and installed Windows 7 Beta 1 build 7000 back in January, your computer is going to start shutting down every two hours starting June 1st, 2009 until August 1st, 2009 when your computer will become non-functional.
Microsoft sent a e-mail to all participants in the public beta stating:
"We're sending this mail to remind you that Windows 7 Release candidate is available and to make sure you plan ahead for when the Beta expires on August 1, 2009. On June 1, 2009, the PC you're using to test the Beta will begin shutting down every two hours. Windows will send you a notice a couple of weeks in advance, and that'd be the ideal time to rebuild your test PC with a non-expired version of Windows, such as the RC or Windows Vista. This will be a clean installation, so be ready to reinstall your programs and data."
With that said it is highly recommended that you download and install the release candidate (RC) that Microsoft released a few weeks ago. Download and upgrade instructions can be found here. The RC build that is available for public download will expire on June 1st, 2010. Just as the Beta 1 release, the RC build will start shutting down your computer every two hours on March 1st, 2010.