Planet of the Blogs now have a ping service available at:
http://www.planetoftheblogs.com/xml-rpc.php
You can update your blog options to send a pingback to the URL with every post.
In WordPress go to:
http://yourdomain/blogpath/wp-admin/options-writing.php (edit URL to fit your setup)
and add a line to point to them:
Planet of the Blogs XML-RPC ping
