You are going to end up with four partitions,
  1. Mountain Lion
  2. Mavericks
  3. Emply
  4. Recovery Drive that is automatically installed by Mountain Lion or Mavericks whichever is installed first.
The Recovery drive partition will not mount or show up on your desktop, but it will be visible in Disk Utility and System Information.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein