The Google build system is written in python. All of Google's corporate code is checked into a repository and the dependency and building of this code is managed by python. Greg mentioned that to create code.google.com took about 100 lines of python code. But since it has so many dependencies, the build system generated a 3 megabyte makefile for it!
Packaging. Google has an internal packaging format like RPM. These packages are created using python.
Binary Data Pusher. This is the area where Alex Martelli is working, on optimizing pushing bits between thousands of servers
Production servers. All monitoring, restarting and data collection functionality is done with python
Reporting. Logs are analyzed and reports are generated using Python.
A few services including code.google.com and google groups. Most other front ends are in C++ (google.com) and Java (gmail). All web services are built on top of a highly optimizing http server wrapped with SWIG.