There are many websites which are stuffed with ads. People may click on ads incorporated within the free content.
However, for decent websites such as StackExchange where ads are placed outside of the main contents on the side, I doubt if there is considerable revenue through CPC.
Instead, reputable websites sell their advertisement space based on their reputations rather than leads. The ads on StackExchange are served by Google, but it is not AdSense (what is it, by the way?).
Is my observation correct or still reputable websites can earn decent revenue by CPC schemes on ads placed on the sidebar?