I don't know about anyone else but what I wanted Path Finder to do was open the documents folder and any other folder in Path Finder not Finder. I tried every suggestion and was a little worried at how intrusive the process was. I discovered a non-intrusive and completely reversible way to achieve the simple tasks I wanted Path Finder to do.
1) Download a program called Default Apps. This goes in your System Preferences and allows you to change what applications can or cannot open.
2) Find the public.folder UTI under the UTI tab in the Default App window [in system preferences after installation]
3)Change the default application from Finder to Path Finder. To do this you will need to change from recommended applications and switch it to any application, but I have scene no problems with Path Finder opening this UTI.

There thats it. To reverse this process simply change the default application back to Finder. Now when I quicksilver documents or applications they open in Path Finder not Finder. YIPEE! Long live the drop stack!

Hope this helps!

I had good luck with this and found that doing the same for public.volume was also good. That intercepts cases like doing a reveal on a freshly downloaded and mounted disk image in the Downloads window of Safari.