We do Google AdSense advertising for almost a year now, that on a shoestring budget, agreed, but the signups and conversion rates are fine. The problem with using just ONE ad-network is, that you just do not reach certain users. Some heavy frequented blogs use the Overture ads and some people, especially in the states, are using the Yahoo search engine. Market estimations range from a 30-50% market share for Yahoo in the states. Google is dominant in most of the world, but the Yahoo services cater especially to people who prefer editorial web evaluation. While Google is working fully automated, Yahoo is looking at the results and tweaks these manually. Therefore we wanted to see, what kind of customer comes from that universe of the web, in which we did not open any "worm holes" yet.
I keep you posted on the outcome in a few weeks.