Priyank Garg of Yahoo! Search today gave a heads-up on a recent change to the Yahoo! natural search index. Yahoo commented -
We've rolled out some changes to our index with fresh web data and updates to our crawling, indexing and ranking algorithms over the last few days. We expect the update will be completed very soon. Throughout this process you may see some changes in ranking as well as some shuffling of the pages in the index.
This is the first update after the launch of Dynamic URL Rewriting in Site Explorer. We've had millions of URLs rewritten based on your submissions and your sites should have seen smarter crawling from Yahoo! Slurp as a result. You will see further benefits in how your site is represented in the index from this update. Your input improves relevance and coverage for users in search results, particularly in relation to your site.
Thank you for collaborating with us to improve our understanding of your site. If you haven't yet, login and try out the feature to authenticate your sites.