Yahoo! like Google also has a Research Lab. Their newest search tool is called Yahoo! Mindset.
Yahoo! Mindset allows to sort results based on whether they are more commercial or more informational. A easy to use slider on top of the page allows to adjust the users current preference what kind of results he wants to see on top.
I played with the Mindset tool a bit and it returns interesting results. It can definitely distinct between commercial and non-commercial. I am bit confused on how the ranking within the categorized results are determined as they differ quite a bit from the unsorted list.
More details on the Yahoo! Search blog. Story via Productdose.
Looks like search engine result categorization is en vogue right now. I just reported about a new Google Search Assistant that uses Bayesian to categorize automatically Google results in informational, commercial and spam. Download it here for free.