A few days ago, I tried installing Linux Mint on my MacBook Pro. The whole process was relatively smooth, here is how I did it. For the record, I was installing Linux Mint 16 "Petra" Cinnamon 32-bit, and my MacBook Pro is the non-retina 13-inch, Mid 2012 version. I think the installation process is more or less the same for Ubuntu and other MacBooks. I used this guide provided by the Mactel Team as a general pointer.
I followed the guide on Ubuntu's site here to create the LiveUSB containing Linux Mint.
I used the Disk Utility to create a new partition. Due to the fact that Linux does not recognize HFS, you have to format the new partition as FAT-32.
I downloaded rEFIt from here. Here's a little bit of spoiler - I think rEFIt is not necessary to install any Linux on a Mac. I have not touched rEFIt from start to end, and end up uninstalling it following this guide. If you are willing to take the risk, try to go on without rEFIt and let me know if it works.
Now, reboot the machine. As the machine is starting up, press and hold on to the option key until you see a list of drives/partitions to choose from. Choose "Windows" with a USB symbol on it. Choose something like "Try Linux Mint" when presented with a list of options (instead of "Install Linux Mint").
Now, you should be able to see an icon on desktop to install Linux Mint. Click on it. You will then be presented with a wizard to guide you through the installation process. For me, the installer recognizes that I am on a Mac and asked if I want to keep OS X and install Linux Mint beside it or replace OS X with Linux Mint. I chose the former. After that, the installer also chose the correct partition to install to. Just make sure that that partition is indeed the correct one.