Securityfocus.com has published "Securing MySQL: step-by-step" a guide to locking down your MySQL Server.
"MySQL is one of the most popular databases on the Internet and it is often used in conjunction with PHP. Besides its undoubted advantages such as easy of use and relatively high performance, MySQL offers simple but very effective security mechanisms. Unfortunately, the default installation of MySQL, and in particular the empty root password and the potential vulnerability to buffer overflow attacks, makes the database an easy target for attacks.
This article describes the basic steps which should be performed in order to secure a MySQL database against both local and remote attacks. This is the third and last of the series of articles devoted to securing Apache, PHP and MySQL." - www.securityfocus.com