I just found this article at IBM developerWorks:

'Time-availability maps provide a listing of who is most likely to be available for a certain hour in a certain location. Find out how to use Google Earth and a log of your communications to map and identify the time and place when availabilities match.

Nationwide and international teams, flexible work hours, and four-day workweeks all contribute to change in when and where teams work together. This article presents tools and code to help you find the best times to reach various members of your team across geographical areas using Google Earth. Using a common method of message time-tracking (e-mail headers) and a program to generate Keyhole Markup Language (KML) with appropriate settings, this article demonstrates useful visualization techniques using Google Earth's TimeSpan feature and the "time slider."'

IMHO an interesting idea with room for customization/integration with other systems. As usual with developerWorks articles there is a feedback form at the bottom.

Enjoy

Martin