i think listing site in yahoo directory is important ,but for the question "is it worth it ?"
i think it's changes from site to site, i am getting about 300-500 hits from yahoo dir
and few days ago got to #6 for keyword "sex" in dir search
http://search.yahoo.com/search/dir?p...gle=1&ei=UTF-8 
and i think it will help to get better in google also