robg adds: This works as described, though I'd say it opens Screen Sharing, not Finder.app, by default.

I haven't tried this hint, but I'm not sure that it doesn't go to Finder anyway. Just yesterday, I was trying to set my protocol helper for vnc:// URLs using both More Internet and RCDefaultApp. I wanted to set JollysFastVNC as the helper for that URL type. (Firefox tried to open Screen Sharing.app., which won't work for most of my VNC servers.) Every time I would try and choose Jollys, More Internet would just say there was an error choosing the app, and set the helper app to Finder. Going ahead and clicking a vnc:// link, it does go to Finder, which then hands it off to Screen Sharing.

So, for whatever reason, Finder does seem to want to handle vnc:// URLs, even though it just passes them off.

If Screen Sharing would let you connect to VNC servers that just use a password, and not a username-password combo, I would be happy with it, but as it is, I need to use something else for most of my VNC servers.