Mikel Maron wrote up a small Javascript class to parse a GeoRSS marked XML file and display the points with GoogleMaps. You can see MGeoRSS here. It currently just handles the W3C format for RSS (example of usage for earthquakes).

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In response to his posting to the GeoRSS mailing list, I added a
GeoRSS Simple parsing class.

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Still need to add the full GML spec which calls out boxes, polygons, lines, etc. In addition, the ability to automatically detect and parse the correct format (Atom, RSS 0.92, RSS 1.0, RSS 2.0; GML, Simple, W3C) would be really nice.