I have complained in the past about SP1 setup showing confusing things about services and applications that might cause a restart to be required:
And other users have complained about this reboot in general:
It seems that both of these problems have been "fixed" by hiding the services and applications that are found in the "Check Files In Use" step of SP1 setup. Does this really fix the problem?
After installing SP1, I went to install SP1 CU1 (since I still have to do this in two steps if the instance already exists), and the Rule "Restart computer" failed. So, it seems that after SP1 is installed, even though "Check Files In Use" indicated that no reboot-causing files were actually in use, I still have to restart the computer before installing CU1.
It isn't quite clear during SP1 setup if or why a reboot will be required after installing SP1; in this case, the engine seems to be patched correctly. But I found this in Detail.txt for SP1:
(07) 2012-12-12 06:46:38 Slp: Rule 'RebootRequiredCheck' results: IsRebootNotRequired=True
And then for CU1, run only a few minutes after SP1 was complete, I see:
(07) 2012-12-12 06:53:38 Slp: Windows Update requires a reboot
(07) 2012-12-12 06:53:38 Slp: Rule 'RebootRequiredCheck' results: IsRebootNotRequired=False
So something happened during the SP1 install that set a flag with Windows Update that a restart would be required before performing any more installations.
In addition I've blogged about these issues: