When I bought my boat new and made the decision to have counter-rotating props, my understanding was that having two rights was mostly noticeable when docking and during slow maneuvers. As AKFish1 said, knowing this you could use it to your advantage when the boat "crabs" to one side, but in some situations in a tight harbor it could be a great disadvantage. My dealer also told me there would be a slight performance advantage in terms of power and fuel consumption having the counter rotating. I have no idea if this is true...
Beside the two-prop and initial cost disadvantage of counter-rotating, there is also the fact that if you damage the left lower unit, usually that unit is NOT is stock at the dealers and there can be a longer wait, esp in AK, for replacement unit or parts!