I’ve been able to install it successfully (with some odd quirks) just once, a number of attempts, a number of flavors, a number of CPUs. The main impediment to wider use of Linux is the cliqueishness of its users and developers. In part that’s a consequence of the complete lack of a market incentive (because it’s free). In order to install it on an eMac I use, turns out I’ll have to empty out the data on the hard drive (which isn’t large by today’s standards) but I’m in no hurry, because I have no idea what the next barrier to installation will be.
In my experience it'll be getting Xorg to work with the video card -- though that may not be an issue with Macs as their hardware is much more uniform/predictable than PCs.