Over on the WSI site (and others on which I'm sort of "consulting"), we have "ad issues" (i.e. wish we were making a whole lot more than we are on them!) ... this piece in Advertising Age puts things in an interesting context, and sort of leads the discussion into "virtual real estate" (charging for impressions) actually being more legitimate than charging for clicks.
We're delivering lots of eyeballs (we're currently 73,842nd in the world {out of 185 billionsites} and 15,142nd in the US) ... you would think that we'd be getting more of an income stream from that than we are!