Any reason for navigation? I think for most people, it'* a bit overkill, if you're always going into weird places in your area, or out of it for that matter then you could use it.
It'* probably cheaper to get a standalone Navi, and a seperate Head unit, then you'll also have something that can probably be updated easier, be more focused, and have more features.
Then again a flip out display is pretty slick..
EDIT: and if you have a standalone one, that say mounts on the windshield you can take it between cars.