This is too weird. You can see your screensaver as your Desktop background. Personally this is too disorienting for normal usage, but the exercise illustrates the power of Mac OSX.
CategoryMacOsx CategoryApplescript

tell application "System Events" to "ScreenSaverEngine" is in name of processes

if the result is true then
        tell application "ScreenSaverEngine" to quit
else
        tell application "Terminal"
                if not (exists window 1) then do script ""
                do script "/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine -background &" in front window
        end tell