I just want to inform you that rEFIT is now a dead project. However someone is developing similar project which is now available for Linux/Mac and Windows .
Apple removed superdrive from many Mac computers and the installation of Linux was really tricky for many users. Two days ago I found this program which help you to install Linux on Mac in a really easy way:
In my opinion Canonical should add this program into Ubuntu or publish an information about him on their website.