If you're interested in going eMMC, it's pretty simple from OSX. I got it done in about 15 minutes, and most of that was waiting for the clockwork image to burn. What I did:
Download clockworkmod, repartition zip, reformat zip, cm7 zip, gapps, and oc kernel zip (though if you use the latest nightly you don't need to install the kernel seperately)
Extract the CWR .img file, insert blank sd card into Mac
Open terminal and run the command "diskutil list". Figure out which disk is the SD card. Your HD will probably be /dev/disk0 and your sdcard /dev/disk2, but double check to make sure. You don't want to reformat your HD by accident.
Now run the following commands- assuming your SD card is /dev/disk2, otherwise substitute the appropriate location:
diskutil unmount /dev/disk2
dd if=<drag CWR image here to auto fill in the location> of=/dev/disk2
Now wait. There's no progress bar but the SD card is being burned. Allow about 10 minutes, it's done when the next command prompt line shows up. When it's done, pop the card out then reinsert to mount it. Drag all your zip's onto the card, then eject and put it in your Nook.
Reboot the Nook and it'll boot into clockwork. If you're repartitioning, do those zips now then wipe data and reboot, because you'll probably need to re-register the Nook. Then go back to clockwork and wipe cache, dalvik, data, and flash CM7, gapps & kernel. Don't reboot yet!
Take the SD card out and put it back into your Mac. Open Disk Utility and reformat the card to MS-DOS (FAT32). Then take the card out and put it back into the Nook. Now you can reboot.
That's it! Super easy. At this point I would recommend opening ROM Manager and using it to flash clockwork to the internal memory, makes it easier to upgrade in the future.