Paper: Guide to Cost-effective Database Scale-Out using MySQL
Guide to Cost-effective Database Scale-Out using MySQL by MySQL
This paper is behind a registration-wall, you can't do anything on the MySQL site without filling out a form of some kind, but it's a short, decent introduction to using MySQL for a good sized website.
A Quick Hit of What's Inside
Scale-out vs. Scale Up, Customers using MySQL, Scale-Out Reference Architecture