I haven't seen many, just one of each, but I'd wondered and finally remembered to look them up, thanks Tere!
From Wikipedia : http://en.wikipedia.org/wiki/2+2_(car_body_style)
The 2 + 2 means bucket seats in the front and dual exhaust.
The term 2+2 is a phrase used to describe the configuration of a car with seating for two passengers up front, plus two seats for occasional passengers in the rear. Many vehicles fall into this definition, and there is no official body offering a strict definition, but cars called 2+2s are generally of a more sporting nature than the average vehicle (at least in theory); they tend to have coupé bodies, and sources conflict as to whether they must have only two doors.
Many convertible and targa top cars are strictly within this definition, but are rarely called 2+2s.
While the "plus two" seats in the back are generally not very spacious, they may be effective in bringing down the owner's insurance premium, and are sometimes suitable for children or a dog.
Only a few cars have ever been specifically marketed as 2+2s — most prominent are the classic 1964-73 Ford Mustang Fastbacks, Jaguar E-type fixed-head coupé 2+2, the Lotus Elan +2, the Nissan 300ZX 2+2 and the various Pontiac 2+2 models, including the aerodynamic Grand Prix of NASCAR fame.