Barry Schwartz has reported at Search Engine Land the observation that Yahoo sometimes produces three results from a domain, two of which are indented. In the example [swine flu], the first three results are from "www.cdc.gov".

http://searchengineland.com/yahoo-now-showing-two-indented-results-18073

Example [swine flu]: http://search.yahoo.com/search?p=swine%20flu