We've actually taken a pretty homebrew approach and aren't using any external frameworks - just Tomcat and MySQL. On the hardware side we're using Linode shared servers so that we can quickly and easily scale up or down as needed. The game code is pretty efficient - we've run tests with thousands of players and had no problems, on modest hardware, so we're looking forward to growing quickly!

It's true that we've had some stability issues at times, but we're trying to cover a lot of platforms (Android, iOS, webOS, web) and add a lot of new features to improve the game. Now that we've officially launched (on 10/1) stability will definitely our #1 priority, though.