I know the video above is quite quick, so I would suggest replaying a few times to get a good visual of what I like so much about Lee Westwoods swing.
His swing, particularly in the video, is a great example of how the lower body leads the club down from the top of the backswing.
Many players that I have taught get to the top of their backswing and then try to hit the shot with their arms. This causes them to pull with their arms, release with their hands too early and hit weak, inconsistent shots. It is very important to get your legs and hips involved with your downswing.
Watch how Westwoods left hip shifts from the instep of his left foot at the top of his backswing, to the outside edge of his foot. It is not a big move but it is this 4" shift that is the trigger for the downswing.
When a player like Westwood has relaxed arms throughout his swing, and uses his hips to start his downswing, he can really generate a lot of power and precision.