It seems there are some glitches in Yahoo's algo:
I had registered variation of the main domain (to prevent potential abuse). It had a 301 redirect to the main domain and infact had a URL / "Identified-URL" and various similar (non-standard, I know) meta directives pointing to the "real" URL, EVER SINCE IT WAS ESTABLISHED (easily proveable via archive.org)
The secondary domain had no "real" backlinks (jsut 4 from "whitepages" directories, ie pages that alphabetically list EVERY domain in the country).
The primary domain had hundreds of backlinks (thousands if we count internal ones), incl Dmoz, Yahoo dir, PR6 etc etc etc.
Yet, Yahoo seems to have picked up the "private" URL and shows that in the SERPs instead.
I'm pretty sure that the "primary domain" has a penalty, because despite all its backlinks (Yahoo Dir, dmoz, 100s of independant sites yada yada) when I look for the site's title, it comes LAST in the SERPs, after the "private domain" URLs. And the date-stamp on the cached page is 27-Jan-2004.
On the other hand, Slurp is just as active as Googlebot on the site every day, requesting pages via the "private" URLs, getting 301 redirected and fetching the page successfully.