bill - 5:06 am on May 1, 2008 (gmt 0)

ping [en.wikipedia.org]:

In blogging, ping is an XML-RPC-based push mechanism by which a weblog notifies a server that its content has been updated. An XML-RPC signal is sent to one or more "ping servers," which can then generate a list of blogs that have new material. Many blog authoring tools automatically ping one or more servers each time the blogger creates a new post or updates an old one.

Looking at your feed again, although it validates, it's not really a standard Atom feed [atompub.org]. For example, you're using the RSS <item> [rssboard.org] instead of <entry>. Perhaps you'd benefit from sticking to either the RSS or Atom format.