It's not Yahoo, but MSN that has used LS. They are dropping them this month. If you aren't getting any sales from the clicks, I'd recommend stopping the ads. Actually, that's a good rule of thumb for ANY PPC activity, regardless of who they are or whom they partner with. (Assuming the problem isn't your site, of course, and that you aren't targetting the wrong keywords.)
not all yahoo results uses Looksmart. from what I can see. it is inktomi that uses looksmart result and inktomi provides results to yahoo.. It is a keyword that worth $10 on overture but $0.50 by using looksmart.