I want Linux on a laptop. The bulk of my work involves connecting at the command-line to other systems, sometimes through SSH, sometimes through serial. I like that the same command-line interface for initiating these connections is also the command line interface through which I can manipulate files in the filesystem, edit files through text editors, and manipulate files through command-line utilities.
While usually I can do my work from the office, sometimes I have to work in the field too. It's much easier to have one computer doing that work than it is to have one at the office, one out in the field, and one at home. Unfortunately the newest batch of portable computers, the convertible tablets, don't work well with X-Windows. This means having to have a separate computer at the office to connect into in order to work out of if I want access to everything that is helpful.
I've played with OSX-based laptops, I find the GUI clunky when it comes to working with multiple terminal windows, as Apple has taken the approach of using Apple-Tab to switch between applications, rather than switch between windows. It's more awkward than it should be to switch between multiple terminal sessions quickly. It also doesn't help that Apple has removed important keys from the keyboard, like pgup/pgdn, home/end, back-tab as shift of tab, and the distinction between backspace and delete, so a lot of the keys and combinations that I use effectively aren't available to me on the Mac.