Yahoo
Yes, it is helpful to submit to Yahoo.
Here is info about submitting your site.
Before submitting your sitemap URL, you should submit your home page to Yahoo!. If you do not yet have an account, you will have to set one up before you have access to the submission page.
https://siteexplorer.search.yahoo.com/submit
On the same page, you can submit your feed if you have one.
I found that Yahoo indexed some of my pages and found backlinks faster than Google in the beginning.
Hope this helps.
Gayle Mitchell
writer/publisher