Usability 
Yippy (formerly Clusty) used to be a meta search engine that submited your query to multiple search engines like Google, MS Live, Yahoo, etc. and returns the top hits from all the engines. The current site appears to use a sigle unidentified search provider. Web results are pretty good. Yippy says it does not to track users.
Below the web results there are a large number of links to a paid research site.