I have zero'd out my disk and created a new GUID partition table with one big hfs+ partition for OS X. My partition table looks as such (according to 'diskutil list').
I now get a 'invalid system disk replace the disk and then press any key' error. As far as I know this error is generated by the BIOS emulation module of the EFI firmware, this would mean that it couldn't find a valid MBR on the USB-stick.
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk0
1: EFI 209.7 MB disk0s1
2: Apple_HFS OS X 999.3 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
The previous 'Operating System Not Found' errormessage is part of the FAT32 header so this might mean the macbook could find the USB-disk but not boot from it. Not sure though.