If you have any Wordpress sites this may be useful. I have been suspicious for a while that my newly created posts on all my WP blogs weren't being pinged. I therefore set up a plugin that would allow me to see if I was right and, sure enough, I was. The problem turns out to have been a plugin that was somehow disrupting the auto ping functionality of WP. Before you ask, I haven't pinned down which plugin was causing the problem as I deactivated most of them to see if it was a plugin that was causing the problem.