The build quality is top of the line, the drivers are solid, and everything just works. The trackpad is industry leading, and the keyboard is great too. Performance is exceptional, especially in the 15" which comes with a HQ processor (not ultrabook-grade) and a discrete graphics card. It has a PCI-e SSD. The price is reasonable compared to the competition.
But despite being IMO the best laptop available, the main reason I choose them is because every so often I need to boot into OSX for testing, or to do something Mac-only. And nothing else can do that.