Here is a recent semi-public paper on web server performance mentioned in a message to Tomcat developer mailing list. Download article.zip and read the PDF file inside the zip file. It has some interesting discussion about web server performance myths. Here is an choice excerpt:
[…] yahoo gets 1.5 billion pageviews a day. […]
Yahoo uses 4,500 server to serve up 1.5 billion pageviews each day. If we divide that by the number of seconds in a day, we get 17,361 pageviews per second. Assuming the load is distributed evenly across the servers, each server handles 3-4 pageviews per second per system.
One of the key points the paper stresses is the performance/value offered by hardware XML accelerators for XML-happy web applications. There are other choice bits in the paper, so check it out before the authors take it offline.