If you already have a /usr/local folder and it’s not owned by your user:

sudo chown -R `whoami` /usr/local

Install Homebrew:

cd /usr/local
git init
git remote add origin git://github.com/mxcl/homebrew.git
git pull origin master

This is kind of odd–you install Homebrew right into the base of your /usr/local folder. It nicely ignores other folders that already exists there. Just do it.

Install MySQL:

brew install mysql

Yeah, it’s really that easy. This will take a while.

Now warm it up:

mysql_install_db

And make sure it automatically starts again on login:

launchctl load -w /usr/local/Cellar/mysql/5.1.43/com.mysql.mysqld.plist