I can't check if it's done by location, but when I set my city (Brasília, Brazil), Gmail show me a Sponsered theme from Volkswagen, Voyage car.

My Gmail is in English, but in themes page is set to my city. The theme have an ad in Portuguese (local language).

Anyone can see this too?

I've seen it on GoogleDiscovery two weeks ago, I don't really know if it is a real partnership or anything else...
http://googlediscovery.com/2010/03/19/gmail-ganha-tema-patrocinado/