The Problems With Yahoo!'s Technology • 06.17.08
Since Yahoo! actively edits their search results, they will be forced to edit them over and over.
After they remove a site for spam, it is very easy for someone to duplicate that site (and maybe even use a slightly altered version) at another location.
Yahoo! could also use a bit of coaching on determining the difference between editorial votes and spammy links. Some of my clients outrank their own manufacturers for their manufacturer's brand name in Yahoo!. That is just flat out bad relevancy to make it that easy to manipulate.