Is there a penalty in Yahoo if you have multi-URL's that point to 1 website. Could be 100 URL links pointing to 1 website.
It should be ok if each site has a different IP address... then it will not look like you are purposely pointing all your sites to the same site.
Are you talking about add on domains? And how would each site having a different IP make it better? Same site on different IPs would definitely be duplicate content.
yahoo doesn't care about duplicate content. I hold 9 of the top ten spots for several keywords with exact clones of sites.