Make sure you're using the amd64 image, not the i386 one. Either the netinst or regular CD1 should work fine from a USB stick, if it's amd64. I tried both i386

Make sure you're using the amd64 image, not the i386 one. Either the netinst or regular CD1 should work fine from a USB stick, if it's amd64. I tried both i386 and amd64 about a week ago on my 2011 Macbook Air, and only the amd64 image booted successfully. You shouldn't need rEFIt.