The ping module is useful for notifying interested sites that your site has changed. It automatically sends notifications (called "pings") to the <a href="@external-http-pingomatic-com">pingomatic</a> service to tell it that your site has changed. In turn pingomatic will ping other services such as weblogs.com, Technorati, blo.gs, BlogRolling, Feedster.com, Moreover, etc.