Yahoo! has been gaining ground on Google in the areas of trust and search quality. A large part of this has been due to Yahoo's more open, less secretive nature in the search industry. Several examples of this, including an informative and high-quality search blog, greater respresentation in the forums and a more approachable attitude have given SEOs the feeling that Yahoo!, much more than rival Google cares what they have to say.
Yahoo!'s recent comments on a post at SEW help to illustrate this fact. The sea of automatic blog spam has been plaguing Yahoo's index, thanks to Yahoo! adopting some of what I believe to be the best practices for algorithm development - including a global authority system (similiar to PageRank) and a lower filter on new sites & new links. Yahoo!'s current problems could be solved within a year with forceful effort - primarily growing their index to match Google's size, enabling their spider to reach more web pages and sites more frequently, and eliminating the spam problem.
On a secondary note, Yahoo! Research Labs produces some incredibly revealing and worthwhile white papers on the advancements in algorithm technology. Go take a look - truly impressive stuff.
It's funny how looking back at this old entry, I can see that Yahoo was first to be more open and friendly toward SEO's and Google followed later. Now Yahoo! is planning it's more descriptive site listings feature... Think Google will follow suit? Seems to me like Yahoo! is always trying to outdo Google and Google is always following suit to take away Yahoo's edge...
lol