I am in the same boat - hoping some decent answers come up. I've been looking at a Thinkpad T440s and a MBP 13". The MBP seems a good choice (parallels?) but I don't like that there is no way to update my RAM.
I tried to fully wipe out the OSX partition, which I ended up reinstalling just to get the `bless` command back so I could boot off the drive. Ugh. So it is setup to dual boot now with Refit.
I am quite happy with it otherwise.
I'm not sure how Linux will look with a Retina display, though. That's why I stuck with the non-Retina 13''. The hi-dpi support in Linux desktops is pretty awful.
When I last ran Linux on Mac hardware (several years ago), it was a pretty disappointingly large gap.
It's fine on my laptop (Arch Linux), same as in Windows, but with an i7, GTX 660M and no optimus, and a 15.6" screen there's not much power to save.
You need to make sure that X has the right DPI setting and additionally make some explicit adjustments like resizing the mouse cursor and choosing big icons for everything. Once that is set right, KDE programs work nicely. Some non-KDE programs (such as Spotify) are rendered pixel by pixel the same as on a regular/low dpi screen.
So there are some glitches, but for day to day use it is absolutely workable :)
My big problem is that there is no support for different DPI settings for multiple monitors. This is quite unfortunate and keeps me from using the full resolution on the laptop's display. Right now I run the laptop display at 1680x1050 (still quite a bit higher than the non-retina 13"), which plays nicely with my 27" monitor at 2560x1440.
Besides the display issues, Linux runs great on the MBP retina (late 2013 MacBookPro11,1). Things run more smoothly than my last Macbook (a mid 2010 13" MacBookPro7,1) which had occasional wifi and suspend/resume nvidia issues. The only thing that I can think of that doesn't work is the builtin webcam, which was switched from USB to PCI-E and doesn't have a linux driver yet.
Wayland is supposed actually to fix this but its a little depressing how long we'll have to wait for that.
The install was easy enough. Setting up refit was pretty easy. The only slightly complicated issue was putting the wifi and other proprietary drivers on a thumb drive because the rMBP doesn't have an ethernet port.
My only gripe with this setup is, because I run it about 60% OSX/40% Ubuntu, is that I'm really only happy in Ubuntu when I have a USB mouse plugged in. I haven't figured out how to make ctrl-click equal right click and I'm one of those who likes to two finger scroll inverted (like an iPad), but use the scroll wheel on a mouse in the traditional direction. If anyone has figured out a magic solution to MBP trackpads in Linux, I'd love to hear it.
It looks like the GUI shows options for both devices, but the settings are split between trackpad and device. So it may do what you want.
I attempted Linux on a Chromebook Pixel and it was miserable, which is why I had shied away from the Retina. :-)
Linux support for PC laptops should be pretty decent across the board these days, IMO. Will require some tweaking for things like trackball and trackpad, but otherwise basic system functionality should be there out of the box.
Also, you'll probably want to know about this fix: http://askubuntu.com/questions/50491/detect-touchpad-as-touc...