Here is a quick question for you to think about. Does Yahoo obey NoFollow tags? I think the answer is no, they do not, and here is why.
The basic point of the rel=”nofollow” tag is to prevent sites from passing linkjuice to external sites. This is most often implemented in blogs and forums as a method to prevent spammers from gaining ranking by simply posting for the sole reason of boosting their search rankings.
Google it seems does not count these links as valid, but Yahoo does. How can you find this out? Well you can do this by checking the backlinks in the search engines results using certain syntax, or by going to http://siteexplorer.search.yahoo.com/search?p=yourdomain.com
You will see listed in the yahoo site explorer links from pages that have obvious nofollow tags. That’s about all the proof I need right there.
The next question would be, does Yahoo count these as valid links when giving out search results. This one is a bit more tricky, and I’m not sure if the links count. According to what data I’ve seen in the past few years I would loosely say “yes”.