Someone on Stackoverflow asked where Googlebot crawls from, and I needed a place to put the map. So, here it is:
Your mileage my vary, but in the case of one of my websites, the crawls emanate from Illinois (46.35%), Arizona (15.68%), Wisconsin (14.95%), Virginia (11.85%), and California (11.17%). The web servers that have been subject to these crawls are located in Virginia.
Again, others will have different experiences, but this is what we observed over the course of March 2014.