I had one snap once. The wife was driving the boat, manuevering up to the houseboat, idle speed. Hit reverse to check the speed and it snapped! Fortunately she was going slow enough that the impact with the houseboat was negligable.
Mine broke right at the coupling, inside the boat. It was about 10 years old and I suspect that the alignment was not correct so I wasn't too surprised.
Generally a shaft breaks due to misalignment or an out of balance prop. If your boat is only two years old, and you have never hit anything, then I would suspect that the engine wasn't aligned properly from the factory.
You should at least talk to the dealer, see if he can get some help from the factory.