I'd say without a doubt (in my experience) overswinging is the main culprit. I notice that when I swing smoothly, I get mcuh better results (duh). The key for me is that I don't play enough (once a month) to remember what that feels like. When I have that much of a gap in playing, I think I'm swing smoothly, and have to remind myself to swing even slower. Other issues that I have that have helped score much better over the past year are my set up (aiming the right direction), not trying to get under the ball (let the club do the work) and picking the right club (not going for miracle shot all the time, lay up more often). These three things have easily shaved 7-8 strokes off.