Microsoft appreciates all who installed the Release Candidate (RC) version of Windows 7 to help identify and resolve any issues prior to the general availability of the official Windows 7 operating system, but now it would like you to quit using the RC and get a valid, licensed copy of the actual OS.
As of February 15th Microsoft will begin to not-so-subtly remind you that Windows 7 RC is expiring with frequent warning messages. As of March 1st, your Windows 7 RC system will automatically reboot every two hours–just to keep it fresh in your mind. As of June 1st, Windows 7 RC will only boot to a black desktop and warn you that your Windows 7 is not a genuine copy of Windows 7.
Suffice it to say, time is up and its about to get very annoying–to say the least–to continue riding on the RC version of Windows 7.
Join the party. Upgrade to an official version of Windows 7.