Keith Adams explains how/where/why Facebook uses PHP, PHP's benefits (lack of state/programmer workflow/concurrency), efficient PHP with HHVM, the Hack project for optional typing PHP and much more.
Martin Thompson and David Farley discuss how to use the scientific method to create high performance systems by measuring performance and adapting the implementation to approach the limits of current hardware. The disruptor architecture is an open sourced result of their work at low-latency, high throughput systems for the retail trading platform of LMAX Ltd.
Rich Hickey explains the ideas behind Clojure 1.2's new polymorphism constructs deftype and protocols. Also: Clojure 1.3 features such as faster arithmetic and future features like Pods.