Uninstalling MySQL Community Server on OS X Revision as of Monday, 21 December 2015 at 02:30 UTC

Tested on 10.7 (Lion) and 10.6 (Snow Leopard).

Remove all startup items, receipts and the MySQL installation directory:

 sudo rm -rf /Library/StartupItems/MySQL*
 sudo rm -rf /Library/PreferencePanes/MySQL*
 sudo rm -rf /Library/Receipts/mysql-*
 sudo rm -rf /var/db/receipts/com.mysql.*
 sudo rm /usr/local/mysql
 sudo rm -rf /usr/local/mysql-*

Remove this in /etc/hostconfig

 MYSQLCOM=-NO-

Done.