Shared hosting is huge, many, if not, most, Web sites share an IP address with an other site. The search engines are aware of this. So why do many experts believe that having a unique IP address will make a difference for search engine ranking? that is the topic of a thread at SEO Chat. In my opinion, when linking between sites on the same IP address, or even IP block, it might raise a red flag. Some experts do not want to take this chance and prefer to secure unique IP addresses and even IP block ranges for each domain name they have. It makes sense, if they do extensive linking between the sites within their networks. Otherwise, in my opinion, it will not affect ones rankings in a positive or negative manner.