Susan Athey is a professor at Harvard and Microsoft's Chief Economist. She just did a short radio commentary about online experiments. Here's how it starts:
Did you know that every time you do a search on Google or Bing, you are improving the quality of the search engine? The more people click on a search advertisement from a clothing company or on a link on an online news story, the more prominently it is displayed for the next consumer. And the firms constantly experiment to get things right. They watch what consumers do and adapt their products in response to the results of their experiments.
You can listen to the rest via the Marketplace website.