You started with Java... a language designed to handle credit card transactions world wide. Your story would be very different if you started with say Rails.
If you build stateless horizontally scalable service (and you should) - you are almost always going to be blocked on DB. On the app server front you just keep adding more machines behind load balancer.
As I look back, if we had used RoR or Python we might have moved faster with no negative impact on scale. We would have spent more money on extra servers though!
