I really don't know; maybe I've just been incredibly lucky with mine. It performs flawlessly ( purely subjective impressions on my part...I really don't spend much time with systems benchmarking day to day, so all my comparisons are subjective in nature).
I really have to say, the Air has TOTALLY exceeded even my most optimistic expectations. My friend, and his equally subjective impressions, has ordered himself an Air configured the same way mine is. We actually swapped for a day last week ( yes, I trust him enough to do that) to see if the impressions that we'd formed really stood up in a full day of use.
across the board, every program I used, either platform the performance difference was noticeable. I guess I view that in fairly conclusive terms when much of the "scientific" measuring involves differences of fractions of a second.
When my middle-aged brain can discern a difference in the boot up speeds of a variety of programs, see evidence of one system performing tasks at a faster or slower rate than the other, and see one laptop slowing down with too many open programs and the other still zooming along, I am inclined to say with some certainty that this computer ( the Air) is faster than that computer (the near three year old MBP)
I know that's not the case with a new MBP, or a year old one for that matter ( although I think a year old one would be a case of having to revert to scientific testing much more often than subjective test to discern a difference).
Like nearly everyone else, I'd love to have the fastest one out there. In the Air line, I do, but then there is the MBP line that is almost uniformly superior. That said, I truly do not regret get the Air in any way. I don't feel in the least bit ham-strung by reduced performance for the sake of portability. In the Air I not only have a very full featured, bloody fast and powerful computer, I have that performance in a very light package.
I really see this iteration as a complete "win-win" situation, perhaps for the first time since the Air hit the shelves. I always admired them for the light package, and always felt it a bit unfortunate that they suffered in performance...not a lot...but enough. Now, after a couple of weeks of extensive use of the Air, I am really unsure that I would trade for a more powerful MBP even if I could do the deal for the same price.
Something I've observed is that I am FAR more likely to take the Air with me "just in case" than I was even with my light ( by PC standards), powerful laptop the Air replaced. It is light, but still over a pound heavier than the air. I think that's where the MBP falls down for me...I just wouldn't take it with me nearly as much as I do with the Air.
Plus...I can run both platforms on the Air seamlessly...not something I could do with the PC....but then, you already KNEW that.