I'd like to share my ubuntu + yosemite dual boot experience. In fact, I installed mac osx and ubuntu more than three times until I feel they're perfectly settled. But, I have to confidently say, at least, macbook air is a very ideal choice for ubuntu. Issues such as swapped key on both of my built-in and external apple keyboards are not happened, the keys are perfectly mapped.
I've been following a couple of different guides to install Ubuntu on my Mac. (Mostly this one: https://help.ubuntu.com/community/MacBookPro11-1/Saucy, but I've also been looking into using rEFInd to dual boot. The problem occurs when I boot from my USB. It appears to work fine: my desktop looks like Ubuntu; however, when I go to install Ubuntu, the installer is not finding my Mac OS.