Sativa is spot on. Michael "Angelo" Batio does not use thumb/circular picking, rather he uses more traditional straight up/down alternate picking using his wrist and arm. What's particularly interesting about his technique is that he anchors his hand by placing the last three fingers of his right hand between his pickups, floating his thumb and index finger (with pick) over the strings "like a phonograph needle." (This has actually caused depressions in his guitars between the pickups.)
This was illustrated, as Sativa said, in his Star Licks instructional video from '87, which I have been worshipping since '89. (And, yes, he really DOES ask "how fast can you flick your thumb?")
Getting back to the topic of the thread, a friend of mine is a righteous shredder, and he uses an odd circular picking style. He describes it as such:
Once I get to a certain speed, I still alternate pick but I
start moving my whole hand in small circles, the axis of which being the
string. Going down in the circle I downpick and going up in the circle I
uppick. All of this is done with a very relaxed hand. When I change
strings, my circle-picking follows. It's basically just a mutant form of
Personally, I notice that I do something similar when I use economy picking ... I start to circle to catch adjascent strings on either the upswing or downswing of the circle, but that differs greatly from my friend's technique, which is strictly alternate.
I have never heard of a thumb-flick circular style before ... sounds mighty interesting!!