Google has released CPA ads this week and I believe that this is just 1 step in a process that will lead to a killer model for social networks and dating sites.
I expect at some point sites will be able to feed Adsense or a clone from Yahoo and MSN user data such as Age, Gender, Sex, Zipcode etc of the user viewing an ad. In adwords advertisers can then bid on keywords as well as demographic information such as age, gender, sex etc. Currently companies like ford come in and do a run of the site campaign. Maybe they just want to display girly cars to girls, and guy cars to guys? Paid dating sites are willing to Pay $12.00 a member for Females instead of the $4.00 on average they pay now. There are hundreds of examples about certain demographics being far more valuable then others.
WTF are google, Yahoo and MSN waiting for?