For Christmas 2012, we sailed the Panama Canal on the Island Princess.  When booking this cruise, we chose to chance our luck and booked guarantee (GTY) staterooms.  This means that we booked a GTY stateroom for the lowest category cabin we wanted sail in - in our case, this was an ocean view cabin.  Because we booked guarantee, we didn't get to choose the location of our stateroom, but allowed the cruise line to assign our cabin for us.  By doing this, we saved a little bit of money on our stateroom and were guaranteed to be in at least the category that we booked, and we'd be upgraded if there was availability in a higher level.