A friend of mine told me that big corporations like Yahoo!, eBay, and others have a special agreement with Google where their ads are a lot cheaper than normal. Have you guys heard about that? Do you guys filter out ads from big companies?
keep in mind that advertiser ranking in the ad block is determined by how much the ad pays, AND the likelyhood that it'll get clicked on. i filter 'em out because they base their keyword useage in the ad block on a whole bunch of data, that is sifted and analyzed by people with phds in math their ad copy is designed to generate the most clicks for the smallest amount of money... they aren't much better than mfa advertisers. normal advertisers don't have all that mathematical data to work with, so they don't know how to word the ad to make people click on it, and they end up paying more for clicks... which makes more money for publishers. fyi, ebay has the biggest keyword inventory of any adwords advertiser.