Old Skool T drivers used to setup 1-3mm of toe-in. Theory was that you wanted the windward blade at zero angle when flying hull/blade nearly all the way out. Typically haveing some weather helm applied, putting the leeward blade angled to weather a few degrees, placing the weather blade dead center (due to ackerman effect).
Nowadays, most of the fleet goes with zero toe in.
The ackerman angle is due to the fact that the rudder arms, as they leave the head of the rudder, are bent inward toward each other. When turning, this makes the outside rudder turn less and the inside turn more (in theory because the outside hull is going to need to sweep through a larger radius). Ackerman angle doesn't have anything to do with alignment (EDIT: when pointing straight ahead).
The explanation I've always heard is, as you say, when flying a hull if you watch the windward rudder enter the water; with toe-in, it enters the water cleanly...with them both aligned perfectly straight, you see the rudder enter the water with a degree of misalignment.
My feeling, is that I want both rudders working to steer the boat - not just one. The fact that they both point in the same direction should be a good thing. When flying a hull, the one rudder has to carry the load of the whole boat (imagine what it would look like entering the water)...I would rather have both of them working together resulting in a (slightly) lower angle of attack for both.
