The map above shows the number of Internet user in the world (proportional). Only unclassified choropleth maps are so far supported by the API. Right-click on the image and select Properties to see the URL generating the map image. The URL contains country codes and values for most of the world countries, but the length (1308 characters) is still within the 2083 limit.
You'll find a quick tutorial for making maps with Google Chart API on this page. So far, I find the mapping feature of Google Chart API more suitable for "country highlighting" than for thematic mapping. The maximum size for maps (440 by 220 pixels) is too restrictive, as a world map needs more detail. I also miss a map legend, so the map reader can spot which colours represent high/low values. Still, it's a good start, and a greater advantage of Google Chart API is the possibility to put charts on top of maps.
UPDATE 6 APRIL 2008: A brief tutorial of thematic mapping with Google Charts API
Data source for Internet users: UNdata