Multiple C Class IP Hosting is a well known technique to optimize the interlinking among your websites if you have many. Generally, if you host your all website on a Shared or Reseller hosting account, they are served from the same IP address. It is said that search engines count the backlinks coming from the different Class C IPs but do not count the backlinks from the same C Class IPs. This is still a debateable topic, but the root of the discussion about Hosting on Multiple C Classes is a Google's patent...
Re-ranking component 122 begins by identifying the documents in the initial set that have a hyperlink to document x. (Act 301). The set of documents that have such hyperlinks are denoted as B(y). Documents from the same host as document x tend to be similar to document x but often do not provide significant new information to the user. Accordingly, re-ranking component 124 removes documents from B(y) that have the same host as document x. (Act 302). More specifically, let IP3(x) denote the first three octets of the IP (Internet Protocol) address of document x (i.e., the IP subnet). If IP3(x)=IP3(y), document y is removed from B(y).
On occasion, multiple different hosts may be similar enough to one another to be considered the same host for purposes of Acts 301 and 302. For example, one host may be a “mirror” site for a different primary host and thus contain the same documents as the primary host. Additionally, a host site may be affiliated with another site, and thus contain the same or nearly the same documents. Similar or affiliated hosts may be determined through a manual search or by an automated web search that compares the contents at different hosts. Documents from such similar or affiliated hosts may be removed by re-ranking component 124 from B(y) in Act 302.
The original source of the patent is http://blog.v7n.com/2007/10/02/seo-and-web-hosting/