The price tag.
Don't get me wrong, the MBP does look nice. And plenty of people are clearly willing to throw lots of money at Apple for both the real and perceived benefits of the premium price. But if performance per dollar is my concern --and I'm forgoing the operating system, one of the "real" benefits IMHO-- numerous other competitors blow Apple out of the water.
The point of a laptop is good, light, sturdy industrial design, long battery life, and quality interaction features (solid keyboard, responsive touchpad, good webcam, flat SPL curve on speakers, etc.), while optimizing performance given that. That's what you're paying the Apple premium for, not the OS. Those qualities remain when you run Windows on the hardware.
Out of the frying pan, into the fire...
I have a friend who keeps bugging me about how expensive MBPs are. I asked him to find a better laptop for the money. I care about the following, in order: quality of screen, quality of keyboard, tough case, light wight, long betters life, fast hd, fast CPU, good gfx card. So far no results :) I actually kind of wish there was more choice in the high end market. I have seen a few nice ultrabooks, but they cost as much as a Mac, if not more, so what's the point?
For example, $1000 shoes that last 1 year are reasonable when compared to going without shoes - only $3 a day, and you'll save money that you would have to pay to repair damage to your bare feet.
Could you find a better pair of shoes for less than $1000? Where's the gold leaf, and why do they lace up the front rather than snap up the sides? I think not.
Of course, same arguments can be applied to almost anything, but this thread was about premium laptops. You can't have a premium laptop that's also very cheep.
The X1 Carbon is kind of nice. But same thing applies. Low res screen is a letdown, and by the time you load it up to be comparable to say, rMBP, it's about the same price.