Wikipedia has placed nofollow on all external links, based on my spot check of random entries such as Gregorian calendar, MacGuffin, and Albert R. Broccoli. This change was made with little if any discussion, though there appears to be an effort now to decide whether it should be rescinded.
If this becomes Wikipedia policy, several million external links on 1.2 million pages will no longer contribute to Google's ranking algorithm, and Wikipedia's own pages will get a boost, as Phil Ringnalda describes:
Previously, if you were a certain well-known encyclopedia written as a wiki, you would generate a lot of PR just by having half a million pages, and that PR, along with any from external links, would be distributed around the site by internal links, and would also be distributed to any external sites you felt were important enough to link from your encyclopedia articles.
Now, as a byproduct of antispamming, every single bit of PR that each page has to distribute will be distributed only internally, to your own other pages, since all external links are nofollowed. Net result: you are more popular than before, the sites that you pretend to call important are less popular. You will tend to come out higher in search results, they will tend to come out lower.
I'm guessing this change was motivated by a desire to avoid spam abuse, but the practical effect is a huge site that shares none of the benefit it receives from 139,000 pages that link to its site.
Forgive me if this is common knowledge and I've missed it... but do we know that's how nofollow affects the linking site? I think this is the official word:
From now on, when Google sees the attribute (rel="nofollow") on hyperlinks, those links won't get any credit when we rank websites in our search results.
The unambiguous part is that the foreign site receives no Page Rank. But are we sure that Google acts entirely identically to the link not being there at all? "Page rank" need not be conserved, they could still lower page rank as they normally would without giving credit, and I think that if I were Google, that is how I'd implement it.
I grant that it seems likely that is how it works based on the wording, but it doesn't seem certain. And even if that is how it works today, I'm sure it's a small fix for Google to go ahead and lower page rank for outgoing nofollow links anyhow.
The funniest part is that this is probably doing exactly opposite of what nofollow intended. Wikipedia using nofollow raises the relative relavance of links on most comments sites (which do not use nofollow). Which would you rather trust as an authority on relevance: an encyclopedia, or a zdnet comment forum? This is really pathetic.
I hate to throw in a self-link but this is *exactly* what I predicted would happen:
My focus was on large media/newspaper companies - but this is the same scenario I figured would happen.
Thanks for the link, Karl. I've been scanning Feedster and Technorati looking for nofollow doomsayers, because I don't know enough about Google's algorithm and search-engine optimization to know whether I'm being excessively pessimistic.
You're welcome. I always feel uncomfortable posting a self-link.
Truth be told, I don't know if I'm entirely swayed by either side of this debate either. I'm not sure if anyone, outside of Google, knows enough about their algorithms to know the true effect of this.
A good alternative is to search for wiki sites outside wikipedia. My autism site got some nice inbounds from other wiki pages not associated with wikipedia....and they did not implement the nofollow tag. Of course, I contributed to the content of the page and the site owners rewarded my contributions by keeping my external link up.