I think gojomo has a really good idea here. However, there is no reason to bias it against Google's ad network. We need an advanced search option to find non-ad supported sites, that behind the scenes attempts to filter out every known ad network.
The use case wouldn't be an all the time thing, it would be when you are searching and get results that are overly polluted with ad-based content. Having the option to filter to non-ad based content lets you focus on those sites that have a motivation other than page views for providing content. I imagine this would include both sites actually selling products and non-profit sites like Wikipedia and open source.
Yes, and it could also be sensitive to the screen-area devoted to ads. As in, discard all results where >40% of the above-the-fold area is paid advertisements.
