As far as I had detected in my campaigns (I am in the travel business), I had detected lower CTR in content network than in search. Also an interesting feature I detected is that my conversion is also lower in the content network. I am trying to analyze in deep why conversion rate it's not similar, because even CTR might be low, my conversion rate should be almost the same as in the search engine. If I can find why this is happening, I will let you know.
people in search mode are close to make purchase decsion than those who look at content. Not all content users are driven from search engines. There're more fraudulent clicks in content network than in search. But google's smart pricing should make ads on content network worthy the money.