New answers tagged fastboot
Personally I had to run fastboot as root/sudo for fastboot to detect the device. I tried this on Linux as I don't own a Mac, but it's *NIX anyway ;)
Are you rebooting the device into the bootloader and entering fastboot USB on the bootloader menu? Try: adb reboot bootloader Then, look for on-screen instructions to enter fastboot mode.
For the record: this works fine, so long as you are careful not to flash the userdata partition. I was able to follow the instructions from AndroidPolice for flashing the factory image, including removing the "-w" option from the "fastboot update ..." command (this prevents the update from wiping the userdata partition).
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