tedster - 5:22 pm on Apr 30, 2008 (gmt 0)

It varies throughout time - nothing dependable here. Sometimes the data centers all pretty much the same and sometimes there's wide variation, especially when google is working on a major new initiative. Sometimes a data center can be taken out of rotation for experiments, and you only can access it directly.

The load balancing logic Google uses to determine which data center to tap for any particular query is quite complex - and I don't have any further detail about that.