Can be annoying finding a track but if you click on the position column in iTunes you can put tracks where you like in the playlist and do get used to which number is which song, a little lame though and I was disappointed when I first tried it. However I've had no problems and I don't have to mess about with cd's anymore which is great.
Plus be aware if you opt for sat nav you have to put the sat nav disk in the head unit top use sat nav so the only way to listen to anything bar radio is a cd changer or iPod which you can get allot more songs on and change at will so it's essential really. Again a let down I felt that the maps didn't load onto a memory card.
On the sat nav unit you press CD to get the iPod playlists they come up as CD1 to 6 6 being all tracks I think on the iPod correct me if I"m wrong and it just selects from just playlists. From then on works the same.
A good tip is when you change to the iPod it will keep playing the album you were listening to when you plugged it in under the seat, a good and quick way to get to an album not on your playlists