Here is a gen-u-wine, if amateur, review. I just got the new 2013 Air to replace my perfectly satisfactory 2011 Air. Since I don't deliver the old one to the new owner till tomorrow, I can set them side by side and do a comparison.
First off, they are so alike that I almost wanted to put a sticker on the new one so I wouldn't sell it by mistake.
Second, the new version is most definitely faster - just processor-wise. I had to compile some *nix utilities for the new one, so I thought it would be fun to do it at the same time on the old laptop before I formatted it. All command line stuff.
The difference between them was from 30 to 60 percent, which I don't understand since the procedure was the same in all but one case - just a straight 'make' of downloaded modules from Cpan. Why different source files would cause such a difference on a routine non-graphical task I have no idea.
The 'one' case...
Perl TK has a very extensive test function that builds and destroys screen widgets by the hundreds and very fast. That one completed far faster on the new, which makes sense because of the huge difference between the graphics engines. That one had a difference of almost 200 percent.
One definite difference - the old Air cranked the fan to high in just a few seconds. I have yet to hear the fan on the new one.
I like it.