How does Google treat sites where all external links are no-follow?

Matt's answer:

Today’s question comes from John T. in Denver. John asks: How does Google treat sites where all external links are nofollow? I understand the purpose of nofollow is for webmasters to indicate which links are paid. And I’ll just add, or other links that they don’t want to endorse. But when sites like Wikipedia make every outbound link nofollow, that defeats the purpose. It’s a good question. So just as a refresher on nofollow, it’s a very general mechanism introduced in 2005. And essentially, when we see a nofollow link going from one page to another page, we say this link won’t flow PageRank, and it’s dropped out of our link graph. It doesn’t flow any anchor text as well, so it essentially doesn’t contribute anything in terms of search engine rankings. Now, I think that if you look at what Wikipedia did a few years ago, they switched from having followed links to nofollowed links. A lot of people were doing spammy edits of Wikipedia. You’d seen the same sort of stuff that you saw back on the Open Directory Project, where people would try to subvert the process and get links without the editors, or without people who review those pages, really noticing. So Wikipedia added nofollow to a lot of those external links. And as result, people stopped spamming Wikipedia, at least for PageRank purposes. Now the interesting thing is that, I think Wikipedia could probably follow a slightly more nuanced policy. So for example, if you have a Wikipedia editor who’s made a lot of edits or been a member for a long time, and the edits haven’t been reverted very much, or they’re vouched for by other editors, or whatever your trust metric is, if there’s some reason why you believe that this person should be allowed to make a link that flows PageRank, you could maybe make it so that that particular person, any links that they add to Wikipedia would flow PageRank. I think that you could also imagine things like Word Press. By default, you might have a third-party commenter not being able to flow PageRank, but if you saw that they were leaving really good comments, or maybe over time you trusted their comments a little more, the ability to remove that nofollow so that it does flow PageRank, I think, would be great. So nofollow was fantastic in terms of stopping a lot of the effectiveness in spam. A lot of people spray out a lot of links, but they don’t necessarily have as much effect because of nofollow within our search results rankings. But sites could still be a little more nuanced. I think it would be great, for example, if Wikipedia wanted to explore whether it’s possible to find some links that they trust a little bit more, and maybe some links that are still in a probationary period or that they don’t completely trust. So we’ll see whether that evolves over time, but that’s the general idea about why it might or might not make sense to have nofollow on a link.

by Matt Cutts - Google's Head of Search Quality Team

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