If you have the moment, and you want to get promotion, or get ranked up and what not then Yahoo is definitely one of the best for you to do it in. It definitely isn't a waste of time. Yahoo isn't the only one either, obviously there are different Search Engines. By the way, before you do anything with Yahoo, make sure you know what you're doing. If you want good results you're going to need to research and then invest, don't just throw it away. Good luck.
No Yahoo is not worth it because after the Google, Yahoo is the best search engine and you can also promote your website on Yahoo.
Yes.. Yahoo is always a good place for the SEO and I thought it the best search engines and we will find a good results.