There’s a great article in the current edition of the Human Factors International newsletter that deals with usability issues around online advertising.
The central premise is that the pull of online ads is influenced by:
- Visual impact
- Emotional appeal
- Current need
The issue is, as the user moves through their task path, the importance of each of these factors changes. To pull someone out of the middle of the task path requires ’emotional appeal’. Therefore it’s worth thinking about what ads are placed where:
"Creating visually engaging and clever ads can grab attention. But, taking the next step, understanding what site visitors are focusing on, and how focused they need to be, and then placing the ads at key junctures can both influence the impact of online ads and reduce the negative response to the ads themselves."
I’m not quite sure if it is directly relevant, but this could be one reason why Google’s text ads perform so much better on Google than on the third party content network. A Google search must generally be fairly early on in the task path.