My mistake: I remembered that SL only loaded up the 32 bit kernel, but it looks like it always had a 64 bit EFI. Sorry about the confusion—disregard below. For kicks, I just ran the following terminal command on my MBP 3,1 2.2 w/ Lion installed (10.7.2) ioreg -l -p IODeviceTree | grep firmware-abi I expected to get back EFI32, but here is my result: | | "firmware-abi" = <"EFI64"> I haven't seen any reference to the Santa Rosa based Macs being upgraded to a 64-bit EFI w/ Lion (and I have trolled around a bit), so I am not sure if this is news. I figured I would post it here to see if it is common knowledge. Regardless, I figured the lack of a 64-bit EFI would limit the ability of this generation to run 10.8 when released—if this is true, it doesn't look like that will be a limitation. I apologize if this has been discussed already.