As delivered: Warped front rotor. One headlight cover developed condensation under the lens in rain.
Update at 23k miles: Lifter (valve) noise at low RPMs when engine is hot. I'm told it's normal. Transmission is starting to act up on the 5th-4th gear downshift and I think she's gonna blow! The warped rotor is coming back, and the dealer says the warranty will not cover it this time. Ford must have had something to do with the brakes, as they never seem to be able to get them right (not on the Fords I've owned anyway). My '98 Chrysler hasn't had this problem once in 200k plus miles!
Update at 26k miles: Transmission replaced by dealer under warranty. I was without my car for three weeks, but at least they put in an entirely new transmission rather than let the local monkeys rebuild it. The transmission now shifts very smoothly, but still has some of the same annoying traits (see below) which would require getting rid of the Mazda engineer who thought these were a good idea. A friend of mine with an '05 Mazda6 V6 also has had her transmission replaced under warranty. As much as I like the car, I don't think I would want to buy a used one, unless you get the 4 cylinder, which has a different transmission.
Update at 33k miles: There is a TSB on the transmission. If you buy a 6 with the 6-speed auto make sure it was manufactured after Feb 26, 2006. Mine has a new tranny now (under warranty) and all seems fine. I added a Fujita cold air intake system (US$215 on E-Bay) and the artificial throttle response I complained about below is gone and the engine seems to make more torque now. I don't know why they don't fit this at the factory! Despite the transmission problem, I still really like the car. I wish the transmission didn't downshift when coasting down a hill. Note to engineers: If I want to slow the car down I will use the brakes!
The car handles very well, is fairly quiet and civilized and feels structurally very solid. It's no BMW when pushed hard, but still a very nice car to drive, with a perfect driving position for my 5'11" frame.
The seats feel great around town, but I was a bit less enthralled with them on a 300 mile trip. I can appreciate the difficulty of designing a seat to fit all sizes, shapes and driving styles, so maybe the compromises made were for the best.
I sense a slight hesitation in the engine during low speed, light-to-mid-throttle acceleration. It's hard to say if this is in the motor or just the transmission running through it's six speeds in the few seconds it takes to reach 25 mph. The throttle response also feels a bit artificial. Both of these are a bit disappointing in that I never experienced any driveability problems in my Chrysler Concorde's 200k miles.
Sometimes I wish the Mazda engineers had taken the money they spent developing the 6-speed automatic gearbox and put it towards a little more low-end torque, but the V-6 is very quiet and feels refined.
The vibration in the brakes under hard application is a bit bothersome too. I thought perhaps the pads just needed time to break in, but after 750 miles the problem is still there.
Both interior road noise and the center console are much improved over the '05 version I rented prior to buying my '06.
I did not order the Bose stereo and do not regret it. The standard unit sounds fine. Other than a little more bass in the Bose I had a hard time distingushing the difference.
Update at 3500 miles: The driveability and fuel mileage of the engine have improved greatly with miles (now at 3,500) and the dealer turned the front rotors at no charge which fixed the brake problem. Fuel economy is now averaging over 25-27 mpg (almost all highway miles) compared to 22-24 mpg on the first couple of tanks.
Update at 23,000 miles: The driving position of this car is perfect. It always feels good to get back in it. Forget what I said above about my first impression of the seats. They're great, short or long trips.
Warm weather really slows the car down. Seems like maybe it would really benefit from an aftermarket cold air induction unit.
The automatic transmission shifts smoothly most of the time, but has some annoying traits. An automatic transmission should NEVER downshift more than two gears unless the accelerator is FLOORED. Seems like the programmers were trying to compensate for the motor's lack of torque, but I'd pay money to have someone program this annoying characteristic out. I also dislike that the transmission downshifts to a lower gear when coasting down a hill. That's what brakes are for! Fortunately, putting the shifter in manual mode temporarily overrides these annoying traits, which I do whenever I'm driving in hilly areas.
I've had a valve (lifter) tick when the engine is hot since the car was almost new. Haven't found time to get the dealer to look at it yet but perhaps it just needs adjustment.
I wish the control for the A/C were in the general area of the display. It's annoying to be looking one place and operating a control someplace else whle driving.
The standard Michelin Pilots XSE are holding up well and are AWESOME in the rain. Averaging 26 mpg on the highway and 23.5 mpg overall with the V6 engine.