Linux users -- if: If you're stuck in "waiting for device", make sure you run fastboot as root, such as:
$ sudo ./fastboot oem get_identifier_token
...
(bootloader)
(bootloader) < Please cut following message >
(bootloader) <<<< Identifier Token Start >>>>
(bootloader) C8750A7847621A009AAC7949E9B41A52
...
(bootloader) 7206C18600834B50AB6FA9F4A9AFC71C
(bootloader) <<<<< Identifier Token End >>>>>
OKAY [ 0.004s]
finished. total time: 0.005s
$ sudo ./fastboot oem get_identifier_token
...
(bootloader)
(bootloader) < Please cut following message >
(bootloader) <<<< Identifier Token Start >>>>
(bootloader) C8750A7847621A009AAC7949E9B41A52
...
(bootloader) 7206C18600834B50AB6FA9F4A9AFC71C
(bootloader) <<<<< Identifier Token End >>>>>
OKAY [ 0.004s]
finished. total time: 0.005s