Most people seem to ignore this feature,probably because they don't know about it. PW is planning to make it more prominent, but in the mean time you can easily make your ads look better by adding spacing. Try using 6 - 8 pixels.
Just go to this PW page, click "edit" from the options on the right side of the ad you want to adjust, and the spacing option boxes will appear in the middle of the right hand column on the next page to come up.
You do not have to interrupt your advertisers to make these changes.