I bought a "corporate demo" Speed6, which had been driven by the sales manager of my local dealership.
7,200 miles - Power loss after having the dealer install Sirius and upgraded alarm. Turbo had basically shut down, but car was cold when I picked it up, and I drove it 30 minutes home and 30 minutes back with no turbo at all. This was 7 days after purchase. Quite an omen.
10,000 miles - My brakes started squeaking badly. The pads and rotors were replaced under warranty. (see again at 32,000)
14,000 miles - Electrical issue; driver's heated seat will not deactivate regardless of switch position or even car being completely off with key removed. Caused numerous dead batteries.
32,000 miles - Brake noise reappears and after my insistence pads are replaced and rotors resurfaced under warranty.
32,500 miles - Turbo is blown; large plumes of white smoke pouring out of exhaust after idling. Like a Batman smoke screen. I was literally afraid to back up. Turbo is replaced under warranty.
32,501 miles - Metal on metal ping / significant stutter (gasp) from engine at 3500 RPM. While accelerating at moderate throttle (merging into freeway traffic) during 3rd or 4th gear car would suddenly loose power as if gasping for air and then surge. This was accompanied by a metal on metal clang that gradually got louder over time.
After seeing 4 different dealers, only one would acknowledge the problem, but it was never remedied. I was able to prove that this eventually lead to complete engine failure at 52,000 miles.
52,000 miles - Complete engine failure; rod bent in two places, causing piston to shatter and crankshaft to puncture engine block. Coincidentally it occurred while downshifting from 4th to 3rd gear while braking and slowing for a light. Car shut off just as it reached 3500 RPM.
After almost two weeks of "diagnosis", Mazda accepted liability and replaced the engine (including clutch) for what paperwork said was just under $13,000.
52,200 miles - Car fails to start, but all electronics (wipers, lights, stereo, etc.) are functional. Starter will not even actuate. Dealership blamed this on a bad battery that had been replaced by the dealer only 5 months prior.
52,400 miles - Car vibrates and shuts off while driving. Refuses to restart (identical behavior as issue above at 52,200 miles). This time it is diagnosed as bad coils on new engine.
52,440 miles - Grinding noise in first gear and whining noise in second gear appears. Dealer diagnoses as a "shifted engine mount causing engine to ground out." Whatever that means!
52,441 and on - Dealership tells me that the rear differential is binding. They blame it on different brand tires on front and rear (even though a Mazda dealer gladly installed them and I have the invoice in hand).
What I found appalling is that they use that excuse, yet somehow did not notice this problem in the 6 previous test drives for the other problems in the 3 weeks prior.
I bought a new car a week later, and sold the Speed6 privately for a significantly reduced price, while disclosing all this history and transferring Mazda extended warranty into the purchaser's name. I did run into him a month later though, and he mentioned that the car would occasionally refused to start for hours at a time. It looks like the problems I suffered at 52,200 and 52,400 are still open issues.
I have owned 6 cars now (3 imports and 3 domestic), and have never had any problems even close to this magnitude. I do think many of the problems were exacerbated by poor training of Mazda technicians. I often knew what was wrong while they were still trying the "PCM reflash", which was done a total of 4 times. Only once was it effective.