AdWords Quality Score (QS) is a complex variable that is assigned to each of your keywords and ultimately influences both your ad position and your minimum bids. Exactly how your QS is calculated remains a closely guarded Google secret, but there are still many methods available that will help you improve your QS, and thus your ROI. Here's an easy one to implement that can have a direct impact on lowering your AdWords costs:
The AdWords Learning Center indicates that the QS formula takes landing page quality into account when calculating minimum bids.
Furthermore, the Landing Page and Site Quality Guidelines clearly state that privacy is a factor: