Trying this out, never seems to get passed the "Now unlock your device and confirm the backup operation."
Trying to run it on a Tmo Galaxy S3. USB Debugging is on, I set a Desktop Backup password like it said to. Adb devices lists the phone, so that seems to be okay. Phone is unlocked when I'm trying this, obviously.
I'm sure I am missing something obvious, I just can't think of what.