I own a 2002 Protege, so I don't have blinders on, but there's a lot of emotional hyperbole on this issue.
"Several of my friend's Mazda3's (all under 5 years old) have rust in the rear wheel wells, and the dealer play the "rust is not perforation" get-out-of-jail-free card. Until then, I won't ever buy a Mazda. Too bad. I've owned three of them in the 80's and 90's."
1. Every single car manufacturer works this way. Every car I have ever owned is warranted against perforation ONLY.
2. Cars wear out, if the body quits the same time the rest of the car does, then, like, whatever.
3.100% of rust perforation is due to owner neglect. If i had done chip repair, or the occasional wash + waxing, my car would still be fine ( except maybe for that weird patch on the back hatch under the name plate ). Could Mazda have done a better job ? sure. Did they have a design mistake ? quite likely. Could they have sourced better steel ? possibly. But there's always a tradeoff, and the P5 has been the best car I have ever owned, in every way that matters, and is still a great drive at 12 years old and 300k.
4. That autoblog slide-show posting is pretty suspect. The top 10 worst is actually a top 23, and since there aren't any words explaining the "winners", it's difficult to trust. Hyundai and Kia are (among the ) least likely to rust ? That doesn't correlate to observation, at all.
And finally, it's a P5/M3 rust issue, not a Mazda rust issue, in that I haven't noticed any other models having a problem.