Windows installed another round of updates and now it's asking you to restart. Again. One simple command line entry can disable this obnoxious reminder. Reader Jack writes in with the trick:
To stop this service, open [Command Prompt] (Start>Run>cmd>Enter) and type the following command sc stop wuauserv. This will not prevent Automatic Updates from starting at the next boot. So don't worry, you'll keep getting Windows updates. Just don't forget to restart eventually.