Facebook was in the news recently because they hadn't met revenue projections. Why? Their target users are coming to network and "be social" rather than to buy something. Their ad-based revenue plan is missing its mark.
Another example are spam blogs ("splogs") that steal content from authentic blogs, buy a junk domain, and slap on Google Ads in the hopes of generating revenue. Perhaps some of these nonsense beggar sites do earn a piddly wage, but not to the tune of millions of dollars.
Are we "banner blind"? Yes. Are you stuck in the "Build it and they will come?" mindset? Are you a print advertiser trying to learn the ways of web marketing?
Once you begin to sell ads directly all the old offline knowledge sets come into play. Have you studied how best to adapt advertising theory and practice to the web? To your sites? Just as many webdevs instinctively optimise both for users and SEs, and some for ppc, they should also be optimising their ad offerings, their major revenue streams. You've built it, they are actually coming...now sell some drinks and fast food and ad space...
Cre8asiteforums discusses the topic from all angles in You Optimise For Users And Ses. What about your revenue sources?