As International Auto Show season heats up, it's not hard to shed a tear for all those far-out concept vehicles that never got to see production. Take the Saab Aero X, inspired by the manufacturer's aircraft division, with its lift-off cockpit and panoramic wrap-around front and side glass. It was unveiled in 2006 at the Salon International de l'Auto and was always intended only as a "design study." Maybe it's just as well that it never made it to production?Sean says he recalls an embarrassing incident from the time in which the working Aero X prototype died at a gas station during testing and had to be jump-started. Still, even if the Aero X turned out to be unreliable junk, I'd rather see it on the road than not. I mean, just look at this insane promo video of the cockpit mechanism in action. How about you? What concept cars past do you regret never having been built?