Something a lot of people seem to have overlooked was hinted at in Greg Boser’s comment above. Greg identified that there is a major (and unfair) disparity with how authority sites such as Wikipedia disrupt the linkscape by run-of-site nofollows. Once Wikipedia implemented the no-follows, previously high-value links from Wikipedia were rendered worthless making the site less of a target for spammers. Increasingly large sites are following suit in order to cleanse their own pages of spam. 

If you've read anything about or studied Search Engine Optimization, you've come across the term "backlink" at least once. For those of you new to SEO, you may be wondering what a backlink is, and why they are important. Backlinks have become so important to the scope of Search Engine Optimization, that they have become some of the main building blocks to good SEO. In this article, we will explain to you what a backlink is, why they are important, and what you can do to help gain them while avoiding getting into trouble with the Search Engines.

If you build a new site and only used Domain Authority to create links, you could EASILY have got linked from the worst page possible, even if it was from the best domain, because of the INTERNAL LINKS of the other web pages! How on earth are you going to be able to see the strength of a link if that strength depends on the internal links on an entirely different website?!

Thanks for the clarification, Matt. We were just wondering today when we would hear from you on the matter since it had been a couple of weeks since SMX. I think we’d all be interested to know the extent to which linking to “trusted sites,” helps PageRank. Does it really mitigate the losses incurred by increasing the number of links? I ask because it seems pretty conclusive that the total number of outbound links is now the deciding metric for passing PageRank and not the number of DoFollow links. Any thoughts from you or others?
PageRank has been used to rank spaces or streets to predict how many people (pedestrians or vehicles) come to the individual spaces or streets.[51][52] In lexical semantics it has been used to perform Word Sense Disambiguation,[53] Semantic similarity,[54] and also to automatically rank WordNet synsets according to how strongly they possess a given semantic property, such as positivity or negativity.[55]

If (a) is correct that looks like bad news for webmasters, BUT if (b) is also correct then – because PR is ultimately calculated over the whole of the web – every page loses out relative to every other page. In other words, there is less PR on the web as a whole and, after a sufficient number of iterations in the PR calculation, normality is restored. Is this correct?

Optimization techniques are highly tuned to the dominant search engines in the target market. The search engines' market shares vary from market to market, as does competition. In 2003, Danny Sullivan stated that Google represented about 75% of all searches.[63] In markets outside the United States, Google's share is often larger, and Google remains the dominant search engine worldwide as of 2007.[64] As of 2006, Google had an 85–90% market share in Germany.[65] While there were hundreds of SEO firms in the US at that time, there were only about five in Germany.[65] As of June 2008, the market share of Google in the UK was close to 90% according to Hitwise.[66] That market share is achieved in a number of countries.
Suppose instead that page B had a link to pages C and A, page C had a link to page A, and page D had links to all three pages. Thus, upon the first iteration, page B would transfer half of its existing value, or 0.125, to page A and the other half, or 0.125, to page C. Page C would transfer all of its existing value, 0.25, to the only page it links to, A. Since D had three outbound links, it would transfer one third of its existing value, or approximately 0.083, to A. At the completion of this iteration, page A will have a PageRank of approximately 0.458.
A more intelligent surfer that probabilistically hops from page to page depending on the content of the pages and query terms the surfer that it is looking for. This model is based on a query-dependent PageRank score of a page which as the name suggests is also a function of query. When given a multiple-term query, Q={q1,q2,...}, the surfer selects a q according to some probability distribution, P(q) and uses that term to guide its behavior for a large number of steps. It then selects another term according to the distribution to determine its behavior, and so on. The resulting distribution over visited web pages is QD-PageRank.[41]
Write a description that would both inform and interest users if they saw your description meta tag as a snippet in a search result. While there's no minimal or maximal length for the text in a description meta tag, we recommend making sure that it's long enough to be fully shown in Search (note that users may see different sized snippets depending on how and where they search), and contains all the relevant information users would need to determine whether the page will be useful and relevant to them.

One final note is that if the links are not directly related to the subject, or you have no control over them, such as commentors’ website links, maybe you should consider putting them on another page, which links to your main content. That way you don’t leak page rank, and still gain hits from search results from the content of the comments. I may be missing something but this seems to mean that you can have your cake and eat it, and I don’t even think it is gaming the system or against the spirit of it. You might even gain a small sprinkling of page rank if the comment page accumulates any of it’s own.
Online marketing, also called digital marketing, is the process of using the web and internet-connected services to promote your business and website. There are a number of disciplines within online marketing. Some of these include social media, search engine marketing (SEM), search engine optimization (SEO), email marketing, online advertising and mobile advertising. 

Denver Search Engine Optimization