Last month Google announced a change as to how they handle the rel=nofollow link attribute.
To simplify, PageRank, or link weight, is passed from one page to another through links. To decide how much each link gets the total weight the page has to offer is divided by the number of links on the page. Previously Google, and other engines, removed rel=nofollow links from this equation entirely. Meaning if you used rel=nofollow on your external links, especially those submitted by users such as in blog comments and forum posts, you allow more weight to be passed through your internal links, thus benefiting your site. You can read more about this topic in the above linked post as well as in these two articles: All About Link Popularity & Pagerank; Site Architecture: Optimizing your Internal Links.
The change is that rel=nofollow is added back into the equation, and the weight rationed to the nofollow links simply is never delivered, it goes to the abyss, it is vaporized, never to be seen from again. This change was done quietly around a year ago, Google only just spilled the beans last month, but this would explain the roughly global PageRank drop (where most sites lost PR) that occured back then, all the nofollow links within Wikipedia alone would vaporize a large amount of the Internet’s overall weight.
What this means for site owners is that where you thought you were once conserving PageRank, you’re now just hurting yourself. You should remove all nofollow stamps on all internal links, all of them, and on external links they’re now pointless for link weight conservation.
We can choose to go back to the other methods of link weight retention, methods that we used prior to the invention of nofollow, but many of them are also likely poisoned by this change (such as running through a redirect script blocked by robots.txt) and others have accessibility issues or may be considered blackhat one day.
Instead I immediately thought of a solution that doesn’t aim to block all link weight leakage, but instead aims to mitigate it as much as possible, this is done through two concepts. Depth and link ratios. The deeper a link is in your site, the less PageRank it’ll tend to pass, and the higher the internal link/external link ratio on any given page, the less will be lost.
The solution thus is what I call, Two Step External Links this is really just a visible static page redirect, instead of the automatic redirects that have been used in the past. This type of redirect actually has exists for as long as the Web has, only it was primarily used for liability reasons at government, school, or medical websites where the sites did not want any perceived liabilty for the quality of the content their external links pointed to. What is new is using this method of link for PageRank retention.
Now, you’re supposed to use rel=nofollow on your blog comments and forum posts because you do not exercise editorial control over those links and you do not want to be blamed if they point to bad neighborhoods. But suppose you’re a really good blogger and have a 20 link menu on your blog, but then you make a really good post and get 200 comments on it, all with an external link. If all of those comments are nofollowed, you lose 90% of your PageRank on that page, 90%. If all those links are not nofollowed and not otherwise redirected, you lose 90% of your weight still, and you also open yourself up to the “bad neighborhood” linking liability (plus you’re rewarding potential spammers, thus encouraging more spam, and we hate spam don’t we precious?) If, however, you use my plugin for your blog you recycle 95% of the 90% of weight you’re losing back into your site, meaning instead of losing 90% of your original weight, you’re losing 8.5%.
How it works is, as I explained above, through depth and ratios. You have a visible redirect page that has your fully menu on it and the external link, but since there is just the one link vs your menu (as opposed to 200 vs your menu), it is vastly out numbered by your menu, and so you mitigate the link weight you lose.
I have had developed two plugins for this system. You can download them here. One is for vBulletin, the other is for WordPress. Each plugin has a whitelist so you can exempt certain domains from redirects. Each has a setting to allow the redirect page to itself have a meta refresh redirect on it (to automatically forward after X secondS), and each has a setting to set the external link on the redirect page to nofollow or not (I recommend nofollow). The vbulletin plugin also has a setting to only show it to guests (users not logged in).
The WordPress plugin is really easy to install, just upload it to your plugin directory, the vBulletin plugin requires a few file edits. In both cases if you run other plugins that modify the same parts they may not work, and in both cases it has been tests on both the newest and slightly older versions of the software.
The plugins are free to use, they are in my opinion completely white hat, and both are extremely effective at retaining link weight within your site.
Also both redirect systems are powered with a simply query string and so you can easily send links through them from anywhere else on your site once installed, such as your custom CMS or from within articles where you write the links manually, to then redirect those links as well if you want.