The Mustang hasn't grown very much over the past decade, and has changed very little for the 2+2 passengers that will fit inside. However, the Mustang's grown more comfortable, with better seats and with less noise and vibration than before.
It's still a sports coupe, but the 2012 Mustang is certainly more spacious than, say, the Chevy Camaro, which doesn't have the head or leg room or outward visibility for six-footers. Seating in the Mustang's front seats is low and snug, and sitting upright will bring the driver's forehead fairly close to the windshield frame. Height-adjustable seats tilt and rake, and the Mustang has options for power seats, too, but the steering wheel doesn't telescope. On automatic-transmission models, the brake pedal is staggered much higher than the gas pedal, which we find a little odd.
The back seat remains tight even for small adults, mostly for its lean leg room. Convertibles have less shoulder room, too, so wedging in two adults will take compromise and permission.
Especially as a coupe, the 2012 Mustang is a reasonably practical vehicle, given its performance. Trunk space is pretty good: the trunk opening is decently large, and permits at least one large suitcase and a few other bags to be loaded easily. Convertibles don't lose much trunk space, either.Interior quality has made steady progress in the Mustang, with noticeably nicer plastics introduced in the 2010 revamp. Noise and vibrations of the unwanted type are largely filtered out, but the sonorous engine note in Mustang GTs makes itself known all the time--thank goodness.