Website owners recognized the value of a high ranking and visibility in search engine results, creating an opportunity for both white hat and black hat SEO practitioners. According to industry analyst Danny Sullivan, the phrase "search engine optimization" probably came into use in 1997. Sullivan credits Bruce Clay as one of the first people to popularize the term. On May 2, 2007, Jason Gambert attempted to trademark the term SEO by convincing the Trademark Office in Arizona that SEO is a "process" involving manipulation of keywords and not a "marketing service."
The issue being, this change makes it a bad idea to nofollow ANY internal link as any internal page is bound to have a menu of internal links on it, thus keeping the PR flowing, (as opposed to nofollow making it evaporate). So no matter how useless the page is to search engines, nofollowing it will hurt you. Many many webmasters either use robots.txt or noindex to block useless pages generated by ecommerce or forum applications, if this change applies to those methods as well it’d be really great to know, so we can stop sending a significant amount of weight into the abyss.
A backlink is a reference comparable to a citation. The quantity, quality, and relevance of backlinks for a web page are among the factors that search engines like Google evaluate in order to estimate how important the page is. PageRank calculates the score for each web page based on how all the web pages are connected among themselves, and is one of the variables that Google Search uses to determine how high a web page should go in search results. This weighting of backlinks is analogous to citation analysis of books, scholarly papers, and academic journals. A Topical PageRank has been researched and implemented as well, which gives more weight to backlinks coming from the page of a same topic as a target page. 
Backlinks can be time-consuming to earn. New sites or those expanding their keyword footprint may find it difficult to know where to start when it comes to link building. That's where competitive backlink research comes in: By examining the backlink profile (the collection of pages and domains linking to a website) to a competitor that's already ranking well for your target keywords, you can gain insight about the link building that may have helped them. A tool like Link Explorer can help uncover these links so you can and target those domains in your own link building campaigns.
If you are using Responsive Web Design, use meta name="viewport" tag to tell the browser how to adjust the content. If you use Dynamic Serving, use the Vary HTTP header to signal your changes depending on the user-agent. If you are using separate URLs, signal the relationship between two URLs by tag with rel="canonical" and rel="alternate" elements.
If your anchor text is aggressive and you distribute it the wrong way, your site will be deprived of ranking, and you may get a penalty. Most of your backlinks must be naked and branded. You should be very selective to anchors you use for your website, you can analyze your anchor list with the help of free backlink checker. It helps to understand what to improve in your link building strategy.
Secondly, nofollow is also essential on links to off-topic pages, whether they’re internal or external to your site. You want to prevent search engines from misunderstanding what your pages are about. Linking relevant pages together reinforces your topic relevance. So to keep your topic silos clear, strategic use of the nofollow attribute can be applied when linking off-topic pages together.
I was exactly thinking the same thing what Danny Sullivan had said. If comments (even with nofollow) directly affect the outgoing PR distribution, people will tend to allow less comments (maybe usage of iframes even). Is he right? Maybe, Google should develop a new tag as well something like rel=”commented” to inform spiders about it to give less value and wordpress should be installed default with this attribute 🙂
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?
Another illicit practice is to place "doorway" pages loaded with keywords on the client's site somewhere. The SEO promises this will make the page more relevant for more queries. This is inherently false since individual pages are rarely relevant for a wide range of keywords. More insidious, however, is that these doorway pages often contain hidden links to the SEO's other clients as well. Such doorway pages drain away the link popularity of a site and route it to the SEO and its other clients, which may include sites with unsavory or illegal content.