as of Feb 18th, the Yahoo! Search results are delivered by the Yahoo! Search Technology (YST) engine. YST was developed from the ground up, but did use some information and experience from the Inktomi, AltaVista and FAST. So we no longer deliver "Inktomi Results", though there may be some overlap with what was previously delivered.
I'm still a bit confused, since what I'm seeing from search.yahoo.com in the US at the moment is what looks to me like Google results, whereas uk.search.yahoo.com produces results very close to Positiontech's pure Inktomi search or MSN/Ink search. Is this YST in the US (but very similar to Google) and Inktomi in the UK, or is the google->YST transition still happening? Will US results start looking more like UK results at some point?