2def,
Thanks so much for this guide. With T-Mobile starting their LTE network soon, I wanted to see if I could revert back to 4.2.1 and/or flash the .33 or .27 radio.
This was my first experience with restoring an Android device. I have to say, though, it was touch and go for a while; like the other Mac users, I kept getting "ERROR: usb_write failed with status e00002be FAILED (data transfer failure (No such file or directory))" when trying to write system.img. I tried all of your tips in the troubleshooting section, tried to flash it a number of times, even going so far as to fastboot reboot-bootloader between each and every step. Absolutely nothing worked.
I ended in a really bad place; I got a warning that I was in "Download Mode." I tried resetting it a few times but it went back into "Download Mode."
I finally was able to get back to fastboot, and, since I was having so many problems with OSX, I booted into my Windows bootcamp partition, followed each step EXACTLY and, lo and behold, I now have a factory 4.2.1 image running.
Thanks so much.
Audio