Google for overhead squats and out of 8 billion pages or so, guess what comes up?
Our very own Dan John's site. With an excellent article about my new favorite lift.
After reading about his experience with the lift, I had a go at them last night. If you've never tried them before, definitely "just" add a few in...be ready to be surprised.
An interesting aside--after doing the OH squats last night, the FRONT of my calves (the muscles to the outsides of my shin bones) are sore as HELL. Weirdness...I've never gotten that area sore before.