COM Objects designed just for scripting purposes only are more forgiving to just overlaying the DLL and not re-registering. But when new functionality in terms of new objects are added, re-registering is a good thing and prob required. If just Automation methods and properties have been added, overlaying works ok (do it all the time). Like Jooel says, if objects have been ripped-out, un-registering should be done to clean up. But mostly that doesn't happen.