Steve Ollington is a Mozzer with a great reputation. He has taken the class and spoke very highly of it for advanced SEO training. Below is an article Steve wrote where he reviewed numerous training courses.

http://www.davidnaylor.co.uk/seo-training-courses-for-seo-certifications

@Klarke, that WBF video addresses "link diversity" which is a related but separate topic.

IP diversity would address links coming from separate IPs.

Often a site owner, especially on shared hosting plans, have a single IP. They can host literally dozens of sites with that IP. When multiple sites link from the same IP, it is an indicator the links are not "independent votes" but rather the same site owner repeatedly "voting" for the same site.

In the early 2000s site owners were able to manipulate rankings in this manner. In the mid 2000s, search engines caught on to this type of scheme and began looking for IP diversity. Multiple links from the same IP were treated as less valuable or the links were devalued almost completely.

In the late 2000s, the concept of "C-block" diversity became important. IPs take the form of numbers such as XXX.XXX.XXX.XXX where the numbers are seen in the format of AAA.BBB.CCC.DDD. An IP of 150.76.44.255 would have a C block of 44. When IPs were assigned to various web hosts, the C block mostly remained constant.

Around 2010, search engines further evolved to keep up with the times. Presently it is easy for anyone to acquire a range of completely different IPs on the same server. Deeper analysis is required to catch manipulation from the same site owner. For example, often the nameserver will reveal other sites on the server, but that information can be manipulated as well.

The concept of IP diversity should not be thought about unless you are venturing into black hat SEO in which case your efforts will likely fail. For the relatively few people who get away with it nowadays, there are tons who are caught.