From Windows Team Blog post at http://windowsteamblog.com/blogs/springboard/default.aspx
“Still on the Windows 7 Beta,? You need to move to the RC and fast. Starting July 1st, the Beta will start to reboot every 2 hrs and expire Aug 1st.
Want to download the RC? . The RC download program closes August 15th. After that, you won’t be able to get the download, but you can still install the RC and get a key if you need one. (To get a key, just go to the Downloads page and follow the instructions.)
If you’re using the Windows 7 Release Candidate, we hope you like what you see. Let us know — go to http://input.microsoft.com and tell us what you think. You’ll be able to give feedback on various aspects of the operating system.”