I thought this was interesting; a compilation of riders who almost made the Rnickey Mouse Mulholland crash highlights reel.
Close Calls Compilation (http://www.youtube.com/watch?v=tNcZyDSM6GI#)
The most common thing I'm seeing (and hearing) is chopping the throttle when the rear wheel steps out, particularly at the beginning of the video. What else?
Stiffening up and forgetting to look and/or push the bars in the direction you want to go - running wide.
[beer]