I tried this to and got the same results.
I've reset my Lumia 920 twice and both times it got stuck on the gear-spinning logo.
The first time, I let the battery drain completely and kept powering it on until it wouldn't power on any more. Then I charged it and it came back to life.
Today I reset it, got the spinning gears, and thought I was going to have to do the same thing. I ended up doing a soft reset (Volume-Down + Power) until the phone reset, then let go of Power. As long as I pressed Volume-Down, the phone would show the NOKIA logo and then reboot. I did this several times. I then pressed and held the CAMERA key until the gears came on. I thought it was going to get stuck again, so I laid it down. About 10 minutes later, the screen flashed and caught my attention, and then the Windows Phone logo appeared and the phone booted into a clean OS.