I noticed if I sat completely upright, my head also touches the roofline, but ever so slightly. Of course sitting perfectly upright is a very awkward driving position, but I just tried it because I noticed how low the roofline was.

BTW I'm 5'11". For everyday driving, I'd fit in one just fine, not sure if my friend could fit or get in and out of the car without much struggle whos 6'7".

Its a great car though, I just felt cramped in one and yes the backseat is only fit for toddlers and midgets...they should've just made it a 2 seater.

I sat in one before I made the decision that I was absolutely positive that I wanted a sedan so no this isn't me making a comment on it because I'm jealous that I don't have a G37 or anything.

 

On my G35 coupe, unless I lean the seat back much farther than where I'm comfortable, I also hit my head on the headliner. I'm 5'11", but my pants inseam is only 30". No matter how I adjust the seat I have this issue.

 

This is why I got the sedan. I had this problem on a 2004 coupe. "Proper" sitting position means your tail is flush against the back corner of the seat so your lumbar isn't "slouching". This is especially important for people with back issues (like me). I'm sure not everyone sits like this, which is why you have people claiming no issues at 6'+ tall. Then there's always the torso-length thing.