I'm working as a bit of a webmaster for a guy that runs a network of backlinked websites to increase his PR for a couple of his eCommerce sites. I don't know much about them, I just know they generate content and funnel the link juice back to where it's needed.
He is hell-bent on making SEO as good as possible on every one of the sites under his network. We have a VPS running about 10 of these sites on a single IP address and he has been struck with the somewhat logical assumption that if Google thought they all came from different servers, as opposed to one, their SEO and pagerank would be better. I'm however a little more skeptical of this idea, as I don't see why on earth Google would consider the content generated from the same server more valuable than content generated from different servers.
In terms of SEO, would a network of sites that link to each other benefit from having different IP addresses? Or could they result in a penalty if they all used the same IP address?