You can always utilize alternate ads, which works quite well if you can find one that covers all aspects of your site's niche. Google also released a way that if only PSA are displayed, then you can display a solid color background in place of the PSAs, such as the color of the table the ad is appearing in. So if the ad is not targeted, your visitor won't get one at all.
Robert
http://www.pcprofiles.com
PC Profiles and hardware reviews
Robert
http://www.pcprofiles.com
PC Profiles and hardware reviews