A bit of history - we have been with Adsense since 2005, originally just to cover hosting cost for our sites. Then the program really took off (for us) with substantial revenue (low four figures per month) coming from Adsense. And then came the loooooooong decline. Whatever we tried, adding content, changing ad formats, blocking and unblocking advertisers, all the bells and whistles - it did not do ANY good. The revenues were declining as if on autopilot. In 2009 the revenues were on the level of the hosting costs. Doh!
So we finally pulled the plug on Adsense by the end of 2009. No need to uglify our sites with Adsense when there is no money to be made.
Consequently our sites looked squishy-clean again (except for that odd affiliate link here and there). Guess what? Since spring 2010 we are getting inquiries from direct advertisers (and SEO types) who are usually nice and easy to deal with. Place a link here, add a set of banner ads there. Money in the bank. Voila: after only few deals we were on the same revenue levels as Adsense gave us in 2009, but with only little intrusion.
It could be our content, it could be that advertisers are getting fed up about "advertising alternatives" (cough), it could be that we are just part of their online marketing mix. I don't know, and honestly, I don't care too much. I like the fact that now the customers approach us with serious proposals, and that we successfully cut out the middle man.
P.S.: Please think of this post as encouragement for those of us who are facing declining revenues month after month. There IS a life after/outside Adsense. :-)