They have 27 locations now, but I believe that major development is still in Denmark: http://unity3d.com/company/people

Yeah, the San Francisco office is now officially the headquarters (moved from Copenhagen in 2009), but as you can see from the bios of the people listed as being in SF on that page, it's almost exclusively the sales and finance office, not where engine dev takes place.

I didn't know that. That's one piece of technology that has made a considerable impact on modern gaming.