Stefan Kaes has been untiringly pushing for optimizations of Rails. Since the release of Rails 0.12.1, Stefan has lead an effort that made his own sample application no less than 4 times faster with Rails 0.14.×. Pretty impressive stuff.
Now he’s blogging about Rails performance in general at RailsExpress.blog. So be sure to subscribe to that feed if you care about a faster Rails. He already has suggestions and benchmarks up on sessions and pagination.