Yahoo! Mindset is a search demo that lets you sort the results with a slider that lets you choose the weight of “commercial” against “research”. I assume they look at the source of the link. Thanks to Matt Patey for this.
A Yahoo! Research Labs demo that applies a new twist on search that uses machine learning technology to give you a choice: View Yahoo! Search results sorted according to whether they are more commercial or more informational (i.e., from academic, non-commercial, or research-oriented sources).