Today I seen a bizarre problem with the search function of Windows XP SP3.  Regular users couldn’t use the search function from the Start menu.  When selected, it wouldn’t do anything.  However, it would work from an Explorer window.  Users with Admin access always worked.  Fortunately it would register an error in the System event log each time the the user tried to do a search.  The unfortunate part was that event log error wasn’t obvious.  It would register EventID 10016 DCOM error indicating that:

The machine-default permission settings do not grant Local Activation permission for the COM Server application with CLSID {blah blah blah}

Searching through the registry for the CLSID returned which COM server application it was and once we granted users Local Activation to the correct COM server, regular users were able to search off the Start menu.

See this as well regarding DCOM security: http://msdn.microsoft.com/en-us/library/ms679714(VS.85).aspx