I purchased one car through Carmax years ago, and I would say it was a good experience. The only issue I had was with one of their asshole service guys, but they even made that right for me.
When there were issues with the car they took care of it and gave me a loaner car.
It was nice to go in and not have to do the price dance and deal with all that shit. Even more so when I compare it to my purchase at Toyota Direct, that was the single worst bying exeperience ever.
That beign said, my next purchase will be through Jet Auto...