[InclinedPlane]

Ads that ask for money: the readers are wikipedia's customers.

Ads that make money: the readers are wikipedia's product.

Incentives matter.

[matthewj]

A good reminder to always pay attention to who/what is actually the product.

[po]

I was going to say exactly this. Who you take the money from is the most important part of this. Even if the site ends up looking exactly the same, it aligns your interests with the reader's.