I'm not sure it would be benificial to penalize multiple domains on the same IP address for cross-linking. In my case, I have a leased server with 1 IP address, which I use to run several sites on different domains. Many of these sites link to each other. Does that mean I'm cheating and trying to create false linkage? No! The links exist because they are related sites, and help with navigation between my various projects. I would imagine others out there have the same setup.