MaxPunkte Streckenflugauswertung is a German GPS tracking tool optimised for hang gliders, the most recent versions of which converts to KML as well. There certainly is no shortage of such converters these days.
Google Sightseeing is the first blog (that I know of) to do something I think will become ubiquitous: Provide a site KML file in addition to an RSS file, as a matter of course.
It makes most obvious sense for a site devoted to places as viewed via Google mapping technology, but all blogs that at least occasionaly post content involving locations should consider publishing KML feeds; they provide another way into the site — Google Earth users who subscribe to blogs’ KML feeds to surf geographically. A trivial example: One blogger might review one restaurant, another might review a competitor around the corner; GE makes the link explicit.
Over on the Keyhole Community bulletin board (Keyhole is what Google Earth was called before Google bought it and made it free), somebody has converted GPS data of live locations of public transport buses in Boulder, Colorado, and turned them into a KML file that updates in real time. Great proof of concept.
Got some coordinates you’d like to place on Google Earth? Here’s a KML Generator. Very easy. Very cool.
For reference’s sake, full documentation of KML 2.0, Google’s XML for placing things on their Earth.
Courtesy of Google, a tutorial on the structure of .kml files, those xml files that contain the placemarks, paths, overlays, etc…