Over the last few months, Yahoo has been upgrading their ranking algorithm and making it so it’s more difficult to rank with sheer spam.

Here are a few things we’ve been observing:

1. Many of the top ranking sites have many links from directories.

2. Number of links from unique domains seems to be more important now than before. For example, you may have 10,000 backlinks, but if 8,000 of those links are from the same domain, you really only have 2000 unique domains. They are collapsing multiple links from one site and counting them as just one link.

3. They seem to be favoring sites that have Yahoo directory listings.

4. Anchor density is lower than before. We saw sites ranking with averange anchor density of between 5% and 30%. Rarely did we see sites ranking with high anchor density.

5. On-page SEO seems to be a more important factor than with Google. In some cases, we saw sites ranking where the only advantage they had was better on-page SEO.

6. Title density is as important as ever.

7. Yahoo seems to be favoring sites that have many pages indexed, especially if they are well optimized.

8. They don’t seem to be applying an obvious ageing filter - some sites ranking are pretty new, while some are old.

9. Sites that have old backlinks seem to be getting an advantage. For example, if they have a few links from sites that were registered before 2000, they require fewer links to rank.

10. A couple of links from high page rank sites seem to work magic..with a few of these, you can then have a large quantity of bulk, relevant links, and that pushes a site above others that don’t have the high PR links.

11. Most of the links should be relevant to your site.

These are just a few observations based on research in the Yahoo SERP’s. Feel free to add your own views and observations.