Alex Kochis explained the Windows 7 Beta activation process; Microsoft gives 30 day grace period for activation. If you don’t activate after set up, and click on "Ask me later", you’ll be presented with "Activate Now" on a daily basis until the 27th day, and every four hours after 27 days.
On the 30th day, messages will appear every 60 minutes from the system tray, that reminds you to "Activate Windows Now", a persistent desktop notification that Windows is non-genuine, a non-genuine message that appears when the Control Panel is launched, and the desktop will be set to a plain black background. While you can change the plain black background to any background you choose, if changed the background will reset to a plain black background every 60 minutes. This experience will continue until the Windows 7 Beta is activated. Also, you will not be able to receive optional updates from Windows Update unless the copy of Windows is properly activated.