Christian: I’ve never been happy with the MIME spec either, and Ubuntu’s proposal doesn’t address my biggest issue: Sometimes you want to do something other than “open” a file.
This is a problem we ran into while doing the Beagle UI. If you have an MP3 file, you don’t necessarily want to “open” and play that file right away. Maybe you want to queue the song up at the end of your current playlist. Maybe you want to edit a photo rather than viewing it, or maybe you want to set it as your background.
So what you really want isn’t a MIME type to application mapping but more of a MIME type and action to application mapping. That way we can easily say, “What are the actions we can do with a file of image/jpeg?” and present them to the user, with an application behind it.
You can then extend this to replace the ugly command-line entries in things like gnome-volume-manager. You give devices special MIME types and actions as well. So you could have x-device/x-camera as the MIME type for a digital camera, “attached” or “hotplug” or “open” as the action, and have a .desktop file which handles the action, like launching F-Spot with the appropriate import command-line options.