Dual Boot Linux on Your Mac and Take Back Your Powerhouse Apple Hardware

"A fast, refreshed, and completely awesome Mac is within your reach, but Mountain Lion isn't the way to get there.
The Problem
"When Mountain Lion launched, we were abuzz. It's a great OS, but it's also proof of one creeping fact: Apple is intent on bringing OS X and iOS together. Whether it's by hamstringing system-tweaking apps like CandyBar, making relatively young Macs ineligable for upgrades, or iOS-ifying the operating system (something we've shown you how to fix), Apple is marching towards a single user experience across all of its devices that they dictate, and that you may not particularly care for.
"So what do you do about it? You have this Mac, and the hardware is still solid—but whether you don't like the direction Apple's headed or Mountain Lion is surprisingly slow on relatively new hardware, it just feels wrong to put it in a drawer and forget about it, doesn't it?
...
"One great alternative that will breathe new life into your Mac hardware (regardless of age): Install Linux on it. When you've finished this guide, you'll have set up a dual-boot Mac and Linux system that will allow you to switch between operating systems anytime—meaning it's a low risk way of trying out Linux to see if you might prefer making the full switch on your Mac. I think you might just like what you find..."
Source: LifeHacker
 How to Dual Boot Linux on Your Mac and Take Back Your Powerhouse Apple Hardware