To optimize performance of a web site with a complex application structure, several servers and a world wide user base is quite a challenge. Every site is unique in its set-up so learnings from others have limited value. But there is always something to learn.
Attending O'Reilly media's Web 2.0 Expo in Berlin recently, I had the pleasure of listening to Cal Henderson, who is responsible for operations at flickr.com, the extremely popular photo sharing site. From his presentation "Scalable Web Architectures; Common Patterns & Approaches", I took away quite a few good ideas on how we could improve performance both for abb.com as well as our intranet. Improving performance is not only a question of server set-up, tuning and distribution, but also how the application itself stores and accesses data.
If his 145 slides are not enough, I'd recommend his book "Building Scalable Web Sites". Still want to know more? If so, you should enlist for O'Reilly media's planned Velocity conference in San Fransisco June 23-24 next year, which they claim is a first of its kind. In addition to Cal Henderson, Amazon.com and other global web sites will be presenting.
UPDATE: Cal Henderson is in fact lead developer on Flickr, not responsible for operations.