I've also ridden in the back before. Mind you, it's because I was in no shape to drive but at the time it felt perfectly comfortable.
LOL! That's pretty much the only reason I've ever been in my backseat too. I'm 5'10" & 160lbs. All my friends are around the same height/weight and 4 of us can fit just fine. I could see how someone 6'5" and 250 might be a bit of a squeeze though.