ive had my 08' Coupe for about a month now so i can give you my impressions so far...

i'm relatively short, but stocky 5'6" and i have more then enough room in the back seat (not that i ever sit back there , but i tried for the first time last week)... my buddy is 6'0" and it was a little tight for him, so i think anyone say 5'9" and under will have acceptable head room & leg room... as far as space, its no problem for short - medium rides, say to go out for the night or less then an hour road trips, however i would not want to have to sit back there for say a 4 hour ride to Vegas... leg room is fine as well, and because the middle seat is really just extra space you do have a fair amount of room... theres no center arm rest that folds down so thats a negative, but again, like i said, if it was an hour or so drive, not a big deal...

vs the 4 door, theres a big difference... that same 6'0" friend has an 08' Sedan and ive sat in the back of that thing a few times and theres tons of room there for a typical adult... comparable to my parents E Class.