I have never used a master/slave setup for my mysql databases so please forgive if I make no sense here.
I am curious, let\'s say I want to have a master DB and 3
You should consider using mysqlnd_ms - PHP's replication and load balancing plugin.
I think this is better solution, especially for a production environment, since it's native to PHP and MySQL Proxy is still in Alpha release.
Useful links: