Google's AdSense
 

has anyone tryed ?

yes works well

but its only for non-adult sites

It's too random to be very valuable..

bit of a waste of space on your site, unless you TRY to get people to click on it, which is against their T&Cs.

Adsense is just a way for Google to sell more ads. Its that simple.

They know they have enough distribution to sign up a shit load of affiliates in a small space of time and frankly, even if 99% of those users were paid fuck all..... theyd still host the ads.