Webmasters and SEOs have been recently shaken by an innocent annoucement over at Matt Cutts’ blog (Matt is head of Google’s web spam team): nofollow relation no longer works as it used to, and that’s been the case for over a year.
So what happens when you have a page with “ten PageRank points” and ten outgoing links, and five of those links are nofollowed? Let’s leave aside the decay factor to focus on the core part of the question. Originally, the five links without nofollow would have flowed two points of PageRank each (in essence, the nofollowed links didn’t count toward the denominator when dividing PageRank by the outdegree of the page). More than a year ago, Google changed how the PageRank flows so that the five links without nofollow would flow one point of PageRank each.
rel=nofollow was created in 2005 as a means for webmasters to explicitly condone or condemn the outbound links they implicitly gave credit to. Before nofollow, a page with a PageRank weight of 10 and 10 outbound links would propagate its PageRank to 1 point per link. If a webmaster decided to tag 5 outbound links as nofollow, the propagation would occur on the remaining 5 links only, thus getting 2 point each.
With the “new” approach, the PageRank gets divided by the sum of all outbound links, but only unmarked links get their credit, the remainder points simply getting lost. In our example, this means that although the 5 nofollow links get no points, they still lower the weight of valid ones to 1 per link, with the remainder 5 points lost in twilight zone. In other words, marking links as nofollow does not give more PageRank to the remaining links.
What does this mean? Simply stated, that the PageRank of a given page is divided by the number of links present on the page, regardless of nofollow statements. Effectively coding a link as nofollow only determines whether you attribute it its corresponding points, or cast them away in twilight zone. This has quite some implications on modern websites and CMS online today. A web page allowing user comments sees its PageRank diluted by number of links present in comments, whether said links are spam or not!
It is a sad day when SEOs lose one tool in their arsenal, with no particular viable replacement other than really ugly tweaking, such as comments in a separate page yet served by a frame, or worse, disabling user generated content to keep control. And the web was supposed to get more sociable?