I've Gnome 3.6 under gentoo linux.
When I'm click "open folder" in skype/transmission/firefox download manager
gnome opens it in baobab. I've not found any way to change this behavior
because nautilus doesn't have "open with" page anymore.
Gnome developers are saying that it's a distro-related problem: https://bugzilla.gnome.org/show_bug.cgi?id=687598
*** This bug has been marked as a duplicate of bug 449486 ***