I have a bunch of sites including 4 blogs. The nonblog sites make enough money from Adsense to pay the cost of hosting 20+ sites, 2 dedicated IP addresses and my DSL access. They do that without cutting into my own personal sales through any of the sites.

The click through rate on the blogs is horrible, less than 1/10th what it is on the other sites. I took Adsense off my political blog to make room for other content 'above the fold'. (There's no point in Adsense below the fold - even on the good sites, the CTR for below the fold conten is dismal - about as good as on the blog sites.) Unless your blog has keywords that have extremely high value, the extremely low CTR makes Adsense less useful, in my opinion, for blog sites. On the other hand, my experience with Adsense overall has been excellent and if someone can figure out how to get more clicks out of blog readers let me know.