The good news: I was able to get my machine (a MacBookPro9,1) to boot using EFI. Rather than modifying an existing install, I simply reinstalled Ubuntu using the 64-bit non-Mac live image, which is able to set up an EFI install. (rEFInd can boot this image.)
The bad news: Resuming is still not working. When I attempt to resume from suspend after an EFI boot I do see my desktop background, so I believe that AHCI mode is active, but the system is unresponsive. I filed a separate bug for this at bug #1186818.
Pedro, thanks again for this helpful information.
The good news: I was able to get my machine (a MacBookPro9,1) to boot using EFI. Rather than modifying an existing install, I simply reinstalled Ubuntu using the 64-bit non-Mac live image, which is able to set up an EFI install. (rEFInd can boot this image.)
The bad news: Resuming is still not working. When I attempt to resume from suspend after an EFI boot I do see my desktop background, so I believe that AHCI mode is active, but the system is unresponsive. I filed a separate bug for this at bug #1186818.