Because of the great difficulty I have had getting MySQL to work with Rails on Mac OS X, I decided I would use SQLite instead. In addition, with MySQL's new dual license, I would prefer to use something that has no strings attached. SQLite is a simple file based database system that requires no network. In addition, the source and the binaries are distributed in the public domain. This means you can pretty much do whatever you want with the database and distribute and embed it to your heart's content.

While trying to figure out how to use SQLite with Rails, I ran across this website: How to use SQLite in Ruby on Rails. For my money, this is the most concise, to the point, and accurate site on the subject I could find. I know have Rails working with SQLite on OS X, Ubuntu Linux, and Windows XP. Woot!