I just recently experience DW. Mine was so bad that I had to come almost to a complete stop when it happened. I couldn't do anything but fight the steering wheel, slam on the brakes, and start talking to the man upstairs! It was pretty darn scary in Houston's traffic.
The problem I had was that all my steering linkage was worn out to the point where I could shake it and move everything around. My tires weren't balanced right, my steering stabalizer was shot, and my sway bar links had loosened up. I've had no DW issues since I have corrected all of these problems.