I have become somewhat irregular with this blog. I have got busier with my work and it doesn’t help my energy at all. Writing a good post after a long day and again in front of internet is not an easy task, at least not for a lazy guy like me 
But I have planned to write on this topic for some days now. And yes, Yahoo does support nofollow attribute much like Google. If you add a nofollow tag in a link, Yahoo crawler will index it. But the link will not be considered for ranking of the target page. Here is what they have said officially on their help page:
The Yahoo! Slurp web crawler obeys the rel=”nofollow” attribute for links. Web publishers and blog owners can apply a rel=”nofollow” attribute to any hyperlink on their page to indicate that the link may not be an approved or trusted link.
Note: Yahoo! Slurp may use a “nofollow” link for discovering content, but the link will not be considered an “approved” link for consideration when ranking the target page.
If you would like to read the whole article, click here. So if you have been using nofollow attribute for Google search, you have been automatically taking care of Yahoo too 
