Here are the steps I used to upgrade the BIOS of my Lenovo Thinkpad X1 Carbon Gen 2.
Updating thinkpad bios Flirt grannies
Since the beginning of this year, I'm a happy Lenovo Think Pad T440 user.
All components are supported on Linux (currently running Ubuntu 14.04 on it) — everything Just Worked "out of the box" after the installation.
This has been my experience with all previous Think Pad models so far (I also owned a T42, T60 and T420 before).
The laptop came with Windows 8 pre-installed, which I found very confusing to use (I haven't had actively worked with Windows for quite some time).
But since I replaced the built-in hard disk drive with an SSD anyway (a 500GB Samsung EVO 840), that problem was solved quite quickly.