RSSPing makes a lot of sense. How come no-one is talking about it? Google BlogSearch 16, BlogPulse 34, Technorati 48. As far as I can tell, it started sometime in August (judging by the earliest posts found):
RSS Ping combines RSS item metadata with site update information. It enhances the current ping specification, adding information about exactly what has been updated or published, with the notification that something has been updated. RSS Ping reduces the need to revisit or work done by aggregators and search engines when revisiting the publisher site after being pinged, to provide truly real-time updates for information on the Web.