Comment 10 for bug 388135

I've just filed a similar bug report before I found this report. The problem I reported was that (for me) the part_gpt module needs to be loaded for grub to find the OSX partition. So one possible solution is that grub.cfg should list:

insmod hfsplus
insmod part_gpt
set root=(hd0,2)

the part_gpt module for GPT partitioning, should then give grub2 access to the (hd0,2) partition.

(The hanging blue screen may be because the dsdt.aml acpi/bios file was not properly loaded ... on my machine without the dsdt.aml file properly loading OSX will hang for quite a while at the blue screen, but will eventually load. It seems to be an OSX/SATA issue on my machine.)