I'd suggest implementing memcached before adding a second DB server, often this can help in scaling incredible amounts. We had an application which as soon as

I'd suggest implementing memcached before adding a second DB server, often this can help in scaling incredible amounts. We had an application which as soon as we implemented memcached(we really should have off the bat) the load was cut over 1/2. Of course this was an extreme example since the server was getting pounded with tons of reads from our DB every second.