The large number of pixels on the Retina display (well ... I have it attached to a Thunderbolt monitor too). Ubuntu 13.04 claims they'll support the MBP Retina, but I've already said I want to avoid Unity. I guess that means the drivers are available though. If I was choosing now, I'd probably go for the upgraded Lenovo X1 Carbon (or maybe the 230 ... my son's favorite).

But I also admitted it's usable, so I'll live with it for a couple years.