Slideshare is a good resource for information on scalability. In particular there is a "webapps-scalability" group that has many relevant presentations. For example:
Set Amazon's Servers on Fire
Scaling with Memcached
High Performance Web Sites
Care and Feeding of Large Web Applications
Scaling Twitter
More...
In any event, I'd encourage those interesting in scalability to visit slideshare and peruse the many excellent presentations there.
http://www.slideshare.net/group/webapps-scalability/slideshows