In some of the older stores, you could not even make changes to your description tag on a page by page basis without the help of an RTML'er... the new v3 stores are much more
SEO-friendly and now allow basic users to change the title, keyword and description for each and every page. (Certainly consider upgrading!)
I do not believe that Yahoo is putting more emphasis on meta tags in their search engine - instead I'm fairly certain that it's simply a result of Yahoo listening to their customers and store developers as I was in on some of the calls where they asked the developers what new features they would like to see in the new version. Meta tags seemed to rank high in the list of improvements developers would like to see.
In comparison to the old store versions... the new v3 stores have a lot of
SEO advantages. They brought in the use of CSS and have cleaned up their code considerably. I am very happy with the new changes they have made thus far and hope to continue to see improvements.