From the Windows Team Blog:
Over the weekend, some of you may have received an email from us reminding you that the Windows 7 Beta expires on August 1st, 2009. In that email, we ask that if you are still on the Windows 7 Beta that you should consider moving to a “non-expired” copy of Windows such as the Windows 7 RC or Windows Vista because bi-hourly shutdowns will begin June 1st.
The Windows 7 Beta does expire on August 1st, 2009; unfortunately the date for when bi-hourly shutdowns will begin for the Windows 7 Beta was incorrect however.
Bi-hourly shutdowns for the Windows 7 Beta will begin July 1st, 2009 as we’ve stated both here in this blog post on May 5th and also in the Windows 7 RC FAQ.
Some people seem to have been confused by this. This applies to the pre-RC releases, not the actual RC release. If you haven’t downloaded the Windows 7 RC release, head over and do so now.
http://www.microsoft.com/windows/windows-7/download.aspx