Not the CX9, but I do have a 07' Mazda 3 GT, and love it. Although, the build quality is nowhere near Toyota, and I seriously doubt it'll last half as long. You can really tell around the weld points and edges of the doors and such. It's a bit loud on rough roads due to excessive tire noise "but it's got 17' low profile sport tires, so to be expected". I'm expecting some rattles soon. Engine components aren't tied down very well, and aren't insulated from the frame very well. Pop the hood of the CX9 and check the air intake housing, wiggle it around and see how well it's seated. The 3, isn't seated very well. Easy fix with some rubber feet from Home Depot, but does give you an idea of the engineering.
Nearly 99% of the mechanicals are Ford, from the engine to the tranny. When I'm under the car doing oil changes and such, I see Ford Motor Company stamped everywhere. I'm not sure how much of the CX9 is Ford, but if the 3 is any indication, I'd suspect quite a bit of the mechanicals.
Mazda's are hard on tranny fluid. They don't have big tranny cooler systems, and chew up their fluids in about 15k miles. Folks on the mazda3forum.com site report black fluids around the 10k-15k mark. I changed mine at 19k recently, and it was black as midnight, with a very slight hint of burnt smell. You've got to switch out the oem stuff with good quality fluids, like Mobile 1 full synthetic.
But driving wise, I love the Mazda platform. Very fun, great cruising, and the steering, brakes, and handeling performance reminds me of BMWs. Very tight, whips around corners, and stops on a dime with little effort. I hear the CX9 is set up like that too.
