So far, Ubuntu 14.04 is working flawlessly here on a MacBook Pro with retina display (2012).
Just speaking personally here. I've never been this impressed by a Linux release. If you have an HiDPI screen, then be prepared for a treat. It's absolutely stunning. It's fast, gorgeous, and near pixel perfect. Using the beta over the past few weeks has rekindled the joy and excitement of first discovering Linux as a kid (anyone remember those CDs in the back of magazines?)
The font rendering and window elements are now as sharp as OSX. The new version of GNOME provides integer scaling for all UI elements, not just text. That means no more huge fonts with tiny menu bars. Fonts look even better with anti-aliasing disabled using the gnome-tweak tool (IMHO). After years of tweaking ugly fonts & window managers, and being spoiled by a “retina” display, this is such a refreshing & welcome change to see in a mainstream distribution. After installing the restricted Nvidia driver, Unity is smooth and intuitive. It's clear they've put some effort into fixing the UI annoyances of prior versions.
This was my first time ever installing Linux on a Mac. I've always used a virtual machine. The first attempt using rEFInd was successful, but somewhat tedious. But then I found an easier way.
I installed rEFInd on OSX, booted into the Ubuntu Live Desktop, and then ran the installer with “ubiquity -b”. This worked. But Unity was a bit sluggish. This is because Ubuntu installs the open source version of the Nvidia driver by default (called “nouveau”). I learned the hard way that the restricted Nvidia drivers will not work with this boot method. If anyone else ends up with a frozen black screen, just do an F2 when rEFInd comes up, and add "text" to the boot command. Then you can remove the Nvidia drivers in console mode (although you'll need perfect vision for this, or a magnifying glass).
Now the easy way. The Ubuntu install tool provides several options on the first screen – one of which is to 'Install Ubuntu alongside OSX'.
I booted back into OSX, removed rEFInd, and deleted the Linux partitions - so now I just had the Mavericks partition, followed by free space. Download the Mac version of the ISO & create the installation USB courtesy of Google's assistance.
Now you can simply reboot OSX, hold down the Option key, and select the USB drive. Select the 'Install alongside Mac' option. It will automatically install to the free space. If you need Wifi during the installation, just open the terminal and run 'apt-get install bcm*'. This will load the Broadcom drivers & you'll be able to install any updates. Reboot to your desktop. Now use the Ubuntu software tool to install the Nvidia restricted drivers. Reboot once more, and savor the pixels and speed.
That's all there is to it. I'm going write this up in a blog post, along with some post-install tweaks (enabling the keys for brightness & the keyboard backlight, installing flux, vim/sublime, and remapping the keys in a Mac-friendly way). Just FYI, the various incarnations of Chrome do not yet support HiDPI on Linux. However, the Firefox Aurora version is fantastic (just set the scaling option in the about:config page).