I noticed the same problem as mogadanez: httpCompress will compress static files when run in the Visual Studio Web Developement Server, but not in IIS6 with wildcard mapping set. It does however compress all dynamic requests as expected, including all my extension-less URLs, so the wildcard mapping actually seems to work.

Anybody any idea on what could be wrong here or how to work around it?

I understand it could become too CPU intensive for high-traffic sites to compress a lot of static content on the files (without server-side caching of compressed content as IIS could do it itself), but that’s not an issue for me now.