For those who did not catch it, I was being facetious... And malcolm is correct about the guessing game. It kind of reminds me of a law force who locks you up but doesn't tell you why...
Try it and see what happens to your site. J/K. I think that Google is the only one allowed to sell links. All others will die.
Of course google doesn't penalise them... just search for online directories on google and practically all of them (on the first few pages) will be paid directories. Yahoo is a paid directory, so what?????