Eric Enge Interviews Yahoo's Priyank Garg has an extremely detailed and educational interview with Yahoo's director of product management for Yahoo! Search Technology. Priyank Garg is a great guy - I have known him for the past couple years at least and as you can tell from this interview, he was very forthcoming with information.
- Footer (bottom page links) may not be used for ranking purposes, but will be used for crawling and discovery
- Yahoo uses both human and algorithmic approaches to detect spam and fight spam
- Some spammy sites will still be included in the index but won't rank well, outside of navigational queries (like searching for the site's name)
- Yahoo doesn't automatically discount paid links
- Links in quantity are less important these days
Those are just some of the interpretations of the interview. It is worth reading in its entirety.