Hey Everyone,
I will not not purchase a directory listing in Yahoo for future sites. In my opinion it is a waste of money better spent else where. I have even cancel my anuall renewals for newer sites that I had listed. The good thing Yahoo did not drop them from the directory. Hope that helps some here. 
The Professor is right on about paided inclusion. Eventually sites are spidered/added anyways. As far as giving you better positioning, no it does not help in my opinion.