signor_john - 1:55 pm on Apr 25, 2009 (gmt 0)

It seems to me that advertisers who abuse category definitions may be shooting themselves in the foot, because if their ads perform poorly, they won't get the exposure that they'd get with higher-performing ads. (The situation is similar to that of contextual ads that are designed for branding and not clicking: If advertisers buy CPC ads for "Drink Coke" instead of "Coke to your door, 15c per can," they lose out to advertisers whose ads have higher clickthrough rates.)