How to identify if you have installed WSUS SP1
To identify if you have installed WSUS SP1;
You can check the version number for the wsusservice.exe file located in %ProgramFiles%\Update Services\service\bin\wsusservice.exe.
OR, check the WSUS Build number from WSUSAdmin home page (bottom of the page - Last line)
WSUS SP1 Build 2.0.0.2620
WSUS RTM Build 2.0.0.2472
WSUS RC Build 2.0.0.2340