I've enabled Disqus comments on a site, by entering the site short name into site settings > API keys, and although it appears to be working (I can add comments and see them), the "Verify" tool on the Disqus site http://mysite.disqus.com/admin/settings/universalcode/ is reporting "It doesn't appear that Disqus has been properly installed."

As I say, it appears to be working, so I don't know whether this reflects a real issue or a weakness in their validation method, but thought I'd note it here just in case.