(Apologies in advance if the menu names aren't exactly right -- I'm not using Mac OS X in English, so I'm guessing at the translations.)
I was curious what the "screen sharing" shortcut had in it, so I opened up my
~/Library/Application Support/Screen Sharing/ folder, right-clicked on the "VNC Internet Location" (*.vncloc) file there, and chose "Open With Application -> Other". Then I chose TextEdit.app.
I thought this would open the file (which looks like an XML plist) in TextEdit. Instead, it switches to the Screen Sharing app!
I switched to TextEdit myself, and used File -> Open, and found the *.vncloc file, and it opened as a plain XML file just fine.
Am I misunderstanding how the Finder's "Open With Application -> Other..." works?