Monaro,
This is great information.
There are many who chase pagerank at any cost. Many of these will register extra domains, that they will just use to link to their other sites. As a result, Google is starting to take the IP address of the domain into account in order to cut down on this method.
There are some that are buying extra IP addresses in order to continue with the old method of creating your own cross links.
The idea is not just to get links to your site from other listed sites, and thereby increase your ranking -- by being a relevant related site and having text on your site that matches the keywords in your meta tags.
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