In the time I have spent with my ms6 I have read about all of these problems and experienced none of them myself (except the occasional studder from the fuel pump). Allow me to shed a little light on the quoted complaints.
1) Engine studder- Speculation is all over the place on why this is, but most signs seem to point to the combination of the main fuel pump and cam driven fuel pump (cdfp) attached to the engine. The ms3s have a variant of this problem, but their fuel system routing and tune are a little different. It seems the reason nobody has been able to find a 100% fix to this problem is the direct injected cdfp system configuration is still kind of unfamiliar to most people. Easiest way to avoid this problem is to drive the car the way most every car is meant to be driven and roll into the throttle instead of stabbing it to the floor. Trust me, the car responds well to this and does not lose any of it's fun factor or safety.
2) Clutch- Yes, the clutch is a legitimate gripe. Mazda definitely botched this one right out of the gate, but finally got it right about half way through the first year. It can be taken care of with the TSB, or just look for a late 06 or 07 since they came from the factory with the new clutch setup. Still, even the type A clutch is perfectly drivable, it just doesn't feel like any clutch we as drivers are used to. If a fickle clutch is enough to make a car undrivable to somebody then maybe they are just destined to be paired with an automatic.
3) Turbo failure- This one is easy. There is a great thread with all the information you could ever want to know about the stock turbo on this car... and it has several posts straight from a couple of guys that work for Borg Warner, the company that manufactures the k04 turbo (
http://www.mazdas247.com/forum/showthread.php?t=123728163 The guys from BW get involved about half way through the second page). Responsible modding and proper fluid selection is the best way to avoid turbo problems. If you were considering modding then the turbo solutions range from running thicker oil to a turbo rebuild like the one offered by Protege Garage all the way up through a whole new turbo (that last one gets expensive though).
4) Mod unfriendly- False... Next. No, really, When done in a balanced order this car seems to mod rather well (within reason). Fact is that as of this point this car is not likely going to be a 500hp+ monster or drag strip sweetheart. It's an AWD midsize sports sedan. It wasn't aimed at the extreme tuner market, but still has a fairly respectable aftermarket since it runs the same engine as the ms3 (which has a decent tuner following). If the tune on it is so difficult to figure out then somebody needs to hand Cobb a Nobel Peace Prize in science for cracking that puzzle and bringing us the Accessport.
What I gathered from that guys quotes sounded less like he hated the car and more that he hated the situation he found himself in with the car. Every minor flaw met with anything less than red carpet treatment seemed to be presented as the worst case scenario of how the problem could be. Sure the ms6 isn't perfect, Mazda dealers tend to be a pain in the ass, and this car simply won't put an italian super car to shame in the performance department, but does anyone expect any car to truly be perfect. For what it is (quirks, flaws and all) and what one can be purchased for I think the ms6 is a fantastic car and have no regrets in having bought mine.
About not being able to get one under warranty, how is that possible? Mine was one of the early ones and I still have the factory warranty. Only reasons it wouldn't come with a warranty is if it has unusually high mileage or if the previous owner did something to void it in which case you should turn and run away from that car. Another option would be to wait a few more months and start looking for one of the 07s that will likely be hitting the used market after their leases are up.
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