Demographics typically don't matter that much to traditional direct marketers.
People's actions (what they've bought, what they've searched for, etc.) are much better purchase predictors than people's attributes (gender, race, income, etc.)
Beyond that, online demographic date are often error-prone.
Here a few curious results (27 June 2006):
|Site Demographics... According To MSN AdLab:|
|Google.com||100% visitors female (!)|
|Beer.com||45% visitors female|
|Playboy.com||42% visitors female|
|query: "supermodel"||36% searchers female|
|Ivillage.com||61% visitors male|
|now.org||41% visitors male|