Earlier this month, Matt Cutts shared with search marketers that Google had begun treating nofollow differently, especially in regards to "PageRank sculpting," the advanced SEO tactic that aims to control where PageRank flows around a site.
Today, he goes into detail on how Google views PageRank sculpting, and how it treats the nofollow attribute in regards to PageRank flow.
Cutts offers a simplified description of the PageRank process, where a page's value flows out to the various pages it links to equally. When the nofollow attribute originally came on the scene, Google would just remove those links from the equation, according to Cutts. So if a page with 10 "PageRank points" to share had ten links on it, and five were nofollowed, each regular link would pass two PageRank points.
Cutts today said that Google changed this practice more than a year ago to keep the nofollowed links in the equation, but not passing any PageRank points. So in that same example, the regular links would each pass 1 PageRank point, and the nofollowed links would still "use up" their allotted points, even though they did not pass those points on.
Cutts once again reiterated his stance that PageRank sculpting is not the best way for an SEO to spend his or her time:
I wouldn't recommend it, because it isn't the most effective way to utilize your PageRank. In general, I would let PageRank flow freely within your site. The notion of "PageRank sculpting" has always been a second- or third-order recommendation for us. I would recommend the first-order things to pay attention to are 1) making great content that will attract links in the first place, and 2) choosing a site architecture that makes your site usable/crawlable for humans and search engines alike.
For example, it makes a much bigger difference to make sure that people (and bots) can reach the pages on your site by clicking links than it ever did to sculpt PageRank. If you run an e-commerce site, another example of good site architecture would be putting products front-and-center on your web site vs. burying them deep within your site so that visitors and search engines have to click on many links to get to your products.
There may be a miniscule number of pages (such as links to a shopping cart or to a login page) that I might add nofollow on, just because those pages are different for every user and they aren't that helpful to show up in search engines. But in general, I wouldn't recommend PageRank sculpting.
Why is Google sharing this information now, a year after the change was made? Apparently, they were hoping that SEOs would notice the change and report on it themselves, but they didn't. Then Matt's repeated assertions that PR sculpting wasn't a good use of time went unheeded as well.
One of the biggest ways this affects most search marketers is on pages with user comments that are nofollowed. In the early days of nofollow, those pages would have received a boost over their pre-nofollowed state, since the PageRank taken up by those links would be redistributed by other links on the page.
But as of Google's change last year, those pages should have reverted to their pre-nofollow state, where the nofollowed links did use up PageRank. But with nofollow, those nofollowed links don't share PageRank with other sites, it just dissipates.
But Cutts advises against deciding not to turn off comments to avoid linking out at all:
I wouldn't recommend closing comments in an attempt to "hoard" your PageRank. In the same way that Google trusts sites less when they link to spammy sites or bad neighborhoods, parts of our system encourage links to good sites.