There have been reports that SQL Server 2008 will ask you to reboot after just rebooting. This problem is happening because several applications are marking files in such a way that SQL Server 2008 Setup interprets as a reboot is needed.
If you experiencing this issue, you can add the following command line to the Setup:
You also need to add the Setup scenario to run to the command like. You need to add /Action=Install or /Action=Upgrade to the command line.
You should only use this command line if you are experiencing the issue describe above.
This issue is also documented in Knowledge based article: http://support.microsoft.com/?kbid=2008982