Google's PageRank has proven ineffective against abuse by wikis. PageRank is useful for regular Web sites, but when it comes to the new wave of Web sites run by wikis, PageRank is rendered useless. PageRank is a thing of the past. The Google people didn't anticipate the wiki flood. So it seems easy to abuse PageRank by setting up a Web site run by a wiki, a Web site whose pages are typically highly interconnected and serve as a maze where PageRank gets trapped and confused.
What's bad about this is that the wikis with the most pages are monopolized by Wikimedia. Of the 80 wikis with the most pages, around three quarters are hosted by Wikimedia. This is bad, because it shows that the wiki world has little diversification of hosts. This means high risk for Web users. It means depending on an organization like Wikimedia for most wiki content.
This is why more people should be taught how to host wikis. Sure, not everyone is interested in contributing to the Web's content, but wikis make it easier for people who are already interested. That's what's so special about wikis. They automate the creation of Web pages. After all, that's what computers are for. They're there to perform repetitive tasks and increase productivity.