as the internet progresses and visitors become more and more aware of how to browse a web page, and are also more and more aware of what an affiliate / adsense website looks like, i think banners need to be more and more strategic in placement and design. It is very difficult these days to get valuable click throughs on intrusive banners, i think the best clickthroughs come through creative in content links.
this is obviously a general observation about banners and how less and less affective they are becoming for calls to action. Obviously a site that recieves traffic from great beginner keywords will have more conversion power with banners than a site recieving traffic from “review type keywords will”.
depends on if the user is looking for quick advice or detailed information about something.