From
ZDNet.com :
Three dates RC users need to be aware of:
February 15, 2010
Users start receiving an expiration notification in the task bar once a day
Users will see a Notification Wizard once after four hours and then one time every hour
The OS will continue to operate as normal
March 1, 2010
Task bar expiration notifications continue
The OS will restart every two hours (note that any open documents won’t be saved before the restart)
Between reboot the OS will continue to operate as normal
June 1, 2010
Windows 7 RC effectively expires at this point
The OS boots to a black desktop.
Users are shown a Windows Activation screen informing users that the OS is not genuine
The OS will restart every two hours.