Earlier today Yahoo! Search announced that they will now support the NOYDIR tag, which will work in the same way as the NOODP tag, and prevent Yahoo! from using descriptions from the Yahoo! Directory in search results.
Webmasters who wish to ensure that their own, customised descriptions are used in the search results listings, instead of the editor-written descriptions picked up from the Yahoo! Directory, should place the NOYDIR meta tag in the header section of the pages as follows: