Yahoo doesn't have search anymore. They subcontract to Bing.

Besides, using delicious data would be far too open to SEO abuse.

They can do what duck duck go does and alter the search results or provide extra info. I agree about the abuse, but linking it to your own delicious account or some algorithm for weighing things that is already used for webpages can surely solve that.

Has Duck Duck Go considered directly using social bookmarking sites' informations in their hodge podge of ranking information?