I think that there is still an issue with activating the screensaver via Automator. I've set up an Automator app using the "Start Screen Saver" action, and my logs show that the bug with coreservicesd is alive and well (I'm using an early 2008 Mac Pro, 10.5.2):

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Mar 19 15:58:06 booker ScreenSaverEngine[832]: argument '-psn_0_409700' not understood
Mar 19 16:41:52 booker com.apple.coreservicesd[58]: coreservicesd(58,0xa05defa0) malloc: *** mmap(size=16777216) failed (error code=12)
Mar 19 16:41:52 booker coreservicesd[58]: coreservicesd(58,0xa05defa0) malloc: *** mmap(size=16777216) failed (error code=12)\n*** error: can't allocate region\n*** set a breakpoint in malloc_error_break to debug
Mar 19 16:41:52 booker com.apple.coreservicesd[58]: *** error: can't allocate region
Mar 19 16:41:52 booker com.apple.coreservicesd[58]: *** set a breakpoint in malloc_error_break to debug
Mar 19 16:41:52 booker ReportCrash[853]: Formulating crash report for process coreservicesd[58]
Mar 19 16:41:52 booker ReportCrash[853]: Saved crashreport to /Library/Logs/CrashReporter/coreservicesd_2008-03-19-164152_Booker.crash using uid: 0 gid: 0, euid: 0 egid: 0
Mar 19 16:41:53 booker com.apple.launchd[1] (com.apple.coreservicesd[58]): Exited abnormally: Bus error
Mar 19 16:41:54 booker /Applications/Microsoft Office 2008/Office/Microsoft Database Daemon.app/Contents/MacOS/Microsoft Database Daemon[301]: LaunchServices/5123589: coreservicesd is running an unsupported version, 0 ( we are 10500000 ), so we cannot talk to it.
Mar 19 16:41:54: --- last message repeated 1 time ---
Mar 19 16:41:54 booker ReportCrash[854]: Formulating crash report for process ScreenSaverEngine[842]
Mar 19 16:41:55 booker WindowServer[61]: LaunchServices/5123589: coreservicesd is running an unsupported version, 0 ( we are 10500000 ), so we cannot talk to it.
Mar 19 16:41:55 booker ReportCrash[854]: Saved crashreport to /Users/pweil/Library/Logs/CrashReporter/ScreenSaverEngine_2008-03-19-164152_Booker.crash using uid: 501 gid: 501, euid: 501 egid: 501
Mar 19 16:41:55 booker com.apple.launchd[86] ([0x0-0x68068].com.apple.ScreenSaver.Engine[842]): Exited abnormally: Bus error
Mar 19 16:41:55 booker WindowServer[61]: LaunchServices/5123589: coreservicesd is running an unsupported version, 0 ( we are 10500000 ), so we cannot talk to it.
Mar 19 16:41:55 booker /System/Library/CoreServices/UserNotificationCenter.app/Contents/MacOS/UserNotificationCenter[859]: _RegisterApplication(), FAILED TO REGISTER PROCESS WITH CPS/CoreGraphics in WindowServer, err=-50
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and on and on