I use iphone 4s with proclip right next to my RCD310. With an extension cable of course!
but sometimes its being silly saying that no device is connected...but the good thing is, I can use my phone as nav.
I use a Nexus 7 mounted in the dash with a small Sony headunit mounted behind it. I like to be able to see what is playing. I use to use my iphone and galaxy s3 but it is annoying to rate tracks on them while driving. The tablet also lets me run things like torque and other apps while driving. My tablet is removable.