Wired titled it a killer mashup; I just like that it uses geoRSS and Yahoo Pipes.
Blogger Tony Hirst mixed an RSS feed from Google Calendar with some KML generated using Yahoo Pipes as a middleman, to come up with today’s best mashup: your Google Calendar plotted on a map.
Head over to Hirst’s blog for the gritty details, but the process isn’t too difficult. You'll just need to add the XML output for your calendar (it will need to be a public feed) to the Yahoo Pipe which will then extract the locations and generate a geoRSS feed. Enter that URL in the Google Maps search box and you’ll see all the events plotted out on the map.