I tried everything I could on my Macbook Pro Model: MacBookPro6, Intel Core i5, Boot ROM MBP61.0057.B0F SMC 1.57f18.
First I installed rEFit then I downloaded 'ubuntu-12.04.2-desktop-amd64+mac.iso', then converted it into img using hdiutil (with format UDRW), then I loaded it into the USB key using dd. After reboot... nothing.
Even if I press C, it doesn't load, it doesn't work even with rEFit, what's wrong? How can I get rid of OSX and have my Ubuntu running on this machine?
Don't use ubuntu-12.04.2-desktop-amd64+mac.iso from http://cdimage.ubuntu.com. It's an unsupported release, whose benefits are not clearly communicated on the website ("This image is adjusted to work properly on Mac systems."). The filename suggests to be a special version for Mac, but the image doesn't has a EFI-compatible bootloader (more info), so the only way to boot this image on a Mac is from CD in BIOS-compatibility mode, not EFI mode. Therefore, booting this image from USB stick is not possible.
Try ubuntu-12.04.2-desktop-amd64.iso from http://releases.ubuntu.com instead. This image comes with an EFI-compatible bootloader and is bootable on Mac from CD or USB stick in EFI mode (Tested at this moment on MacBookPro5,5). For booting from USB simply copy the image to your USB stick the way you used to do before.
The tool rEFIt is unnecessary for single LiveCD or LiveUSB booting, but it's helpfull if you plan to have dual or triple boot options on your HDD.
