if you pay the 600 bucks to be in a category which has a few sites only (20-50) then you'll cover the $600 quickly.
if you pay to be in a category that has more than 50 sites, then it will be tough. the first week you get listed, you are at the top of the list with a little "new" next to your site's name: good traffic for 7 days, then after 7 days; you are listed alphabetically (not so good traffic anymore).
the good thing about yahoo listing is that it will better your other search engine's listings.
as far as the bullshit people are saying about the 600 bucks and how tough it is to get in: BULLSHIT
if you submit a site with no illegal shit, in the right category and with no pop up and consoles and other "tricks" then you'll get in the first time
