I've only recently become aware of the registration-free COM activation feature of Windows XP (aka side-by-side deployment). Very interesting. The idea is that you have an application manifest which describes all of the COM types that an application uses. Sort of an application-scoped XML file version of HKCR. Of course, Microsoft has all kinds of caveats about how the COM objects should work to support this mode of deployment, so I'm not sure if it our existing COM API would just work in a production environment. But it could be super-cool for testing different versions of our API on a single machine.
Generating the manifest file is painful for a project with a lot of types, however. Next on the list - write a little tool to generate it automatically by inspecting a type library.