I've got ads rotating on about.com pages, Tucows, and an important forum that gives me great branding for an informational site, and qualified buyers for another website.
I'm constantly on the lookout for those ads that generate thousands of impressions on content spaces, but minimal searches- those are the ones I keep- and dial down to five cents.
You have to weed out the stuff that doesn't work, not only content targetting but negatives etc.
Content targetting can work for you.