Lets put it this way. If you had Linux on the iPhone. You could:
1. Run almost any linux software (probably including all the nice openGL desktops too)
2. Play any format of video or audio that exists.
3. Encrypt your personal data.
4. Probably use wine and run StarCraft, Colin McRae... well basically any game that wine supports and the graphics hardware on the iPhone could handle.
5. Have a full featured desktop environment
6. Basically do anything you wanted to.
If you can already do everything you wanted to, then you dont want much