Hey,
Depends on what you want your i-pad to do in your car?
For music only, the AUX connector alone should be sufficient, yet basic.
That being said, after an hour of use on long trips you would want to have the ability to re-charge while on the go, which would make the USB port installtion a requirement instead of optional, as the cables running from the 12V siggy lighter in your ashtray don't work around the console and gear lever...
Then when you realize how many pedestrians you're about to kill cos you're constantly feeling up and looking at your iPAD instead of the road, you'll want steering controls and integrated display... Nevermind skipping, finding, fwd and rev on tracks....
Then you can debate adding Bleutooth too...and while we're at it, sommer add wifi so you can connect to hotspots while you sit an wait for your KFC drive through order to be done...
Eventually you'll realise that none of the parts for the current model of car you have would support this and you'll start looking at the aftermarket options on e-bay...
You'll read reviews online and find that none of them really suit your needs...
Then you'll start looking at what the new cars do... You'll look at whats in the new BMW 5 series...
You'll speak to your bank manager.
You'll cry...in the shower to soft music.
...and at the end of this you'll be writing CD's with MP3 tracks in your boxers (cause you can make it work). (note CD's, not DVD's as they're not supported)
...then you'll re-write them all with a proper directory structure and better filenames cos "David_Guetta_Remix_1_2008_Ibiza playone.www.mpthreefiles.net.mp3" does'nt scroll nicely on your display....
...but wait, there's more...
You'll then re-build a file structure grouped on 0-99, A-F, G-M, N-S,T-Z because the menu scroll on the head unit won't allow recursive scrolling from Z to A meaning you have to scroll 5 minutes to get to your track you want...
At which point you tune to the local radio stations and make peace with what you have and enjoy the sound of your old 6 cylinder engine and tell yourself that the new four-pot turbo crap is for tree hugging hippies anyways...
Next?