The Google I/O presentations are now online via Google Sites.
Underneath the Covers at Google: Current Systems and Future Directions by Jeff Dean. James Hamilton has a summary online. [Found via Greg].
A single query currently hits between 700 to 1000 servers. Slide 38 from his slides lays out the basic query serving architecture (Index shards + replicas for redundancy and query volume). I'm sure there are more gems here.
I also ran across a few more presentations I'd like to watch:
Effective Java Reloaded by Josh Bloch.
How to Index Your Geo Data by Lior Ron and Mano Marks