Please read this piece about ads on your page, it makes a good point that the ads are part of your brand. And that you should pick them with care, not accept anything a banner farm throws at your site.
Mule Design Studio's Blog: Ads are Content: "The ads you allow on your site are part of your brand."
In fact it was so bad the the load time was multiplied by 5 with banners. FIVE times as long, all because they wanted to track users to better their experience...