Default Applications

1. Open the gnome-vfs mime database, usually at /usr/share/mime-info/gnome-vfs.keys
2. Search for the application type you want to modify (for instance, pdf)
3. Ignoring all the language garbage, find default_action_type= either application or component. Component will try to use one of the items in the short_list_component fields, which are desktop-specific handlers. Application will try to use one of the items int he short_list_applications fields.
4. Set whatever you want to use as the first app in each applications list. For example, pdf might say "acroread,gpdf,xpdf,ggv,gv"
5. You might need to log out for changes to take effect.