Weight has a lot to do with it. The first Macbooks, and the the Macbook Air, were far, far lighter than equivalently provisioned x86 systems. The disparity's gotten better, but you still have HP and Dell putting out boat anchors compared with Apple.
Lenovo's between the two. My T520i isn't flyweight, but it does OK (the power supply is a brick though). I've eyed the Carbon but have passed on it to date.
The Dell XPS 15 [1] weighs around 4.5 pounds, has a higher-resolution display than a Retina MacBook Pro, a comparable i7 quad-core, 16 gb ram, etc. It also has excellent Linux support (source: I have one that I installed Fedora 20 on and everything worked without any tinkering).
There don't seem to be any other options comparable to a MacBook Pro for hardware. In particular, very, very few laptops that aren't enormous and heavy have a quad-core processor.
I'll grant that I may be dissing Dell and HP in part on the basis of their more downmarket and/or "desktop replacement" laptops which tend toward the boat-anchor characteristics.
On a vaguely related note, one aspect of Dells I've found particularly annoying is their implementation of the Trackpoint. While available as an option on some laptops, I found that the rubber used on the nub was harder, and far more irritating to my index finger, than that used on Thinkpads. It's almost comical that user satisfaction could come down to an issue such as this, but over the several months I was using a company-issued Dell, I found that to be a constant annoyance. I tried sanding down the bumps on top, substituting a spare Thinkpad nub (the bases are sized differently, it didn't fit), and a few other tricks. Ended up with blisters on my finger.
I heard many people complain about coil whine in these models. Also does this support GPU switching under Linux and does sleep/hibernate etc work without issues ?
I've haven't experienced the whine myself, but I've seen those complaints too.
GPU switching is the one thing I haven't really tried yet. I've stuck with the Intel chip. I've read that people have had success with Bumblebee. In fairness, I've also had a MacBook Pro with Fedora 19 on it, and GPU switching didn't work there either.
Suspend/resume work without issue, but I haven't installed the proprietary NVIDIA drivers yet, and those have a tendency to mess up resume (at least it did on my MBP w/ Fedora 19).
I _imagine_ NVIDIA drivers + suspend/resume works just fine with Ubuntu. Any "non-free" drivers in Fedora are pretty iffy in my experience. Usually after installing the NVIDIA drivers from RPM Fusion GDM won't even start, or you have to edit the GRUB menu item to blacklist nouveau, or any number of things the package should theoretically take care of for you. I've not had that problem with Ubuntu (just other problems, like a UEFI install on say a MBP, something Fedora does flawlessly).
These are the kinds of reasons people just use Windows or OS X I guess.
Lenovo's between the two. My T520i isn't flyweight, but it does OK (the power supply is a brick though). I've eyed the Carbon but have passed on it to date.