On a typical PC, installing Linux is as easy as putting a CD in the drive and rebooting. But, a Mac is far from your typical PC, and if you insist on running Linux natively, you might be in for a bit more work. Apple is not exactly forthcoming with information, especially with firmware, which makes the job of the distributions that want to support Macs difficult. In addition, Macs from different release years can contain very different hardware, one MacBook is not necessarily the same as another. That being said, once the drivers are installed and the system is configured, Linux on Macs can be a very nice environment, if you are up for a bit of fiddling. This recent Reddit thread reminded me of the many times I've run Linux on my Mac.