We at Black Duck noticed it too. So far, looks like the decline is largely because, lately Ohloh - a) hasn't kept up with discovering new projects. b) hasn't paid needed attention to keeping existing projects up to date.
We'll provide more details once transition is over (we just acquired Ohloh from Geeknet).
As far as I can tell, existing Ohloh features and community will stay as is and will remain free as we add more features and enhance the site. Feel free to email me <username> @ blackducksoftware.com if you'd like to ask any specific questions or have ideas/comments/suggestions.