At the May 2009 Boston MySQL User Group, Giuseppe Maxia of Sun Microsystems gave a presentation about MySQL 5.4 with use cases and benchmarks to show how it outperforms all other current MySQL releases (including the Percona, OurDelta, and Google releases/patches). The slides are at http://www.slideshare.net/datacharmer/mysql-54-theory-and-practice

Sergey from the MySQL Optimizer team talks about recent developments in the MySQL Optimizer, including: What's new in MySQL 5.1 optimizer, Overview of known optimizer problems in MySQL 5.1, State of new optimizations in MySQL 6.0, Optimizer development beyond 6.0