I'm still not a fan of the DBW stuff on the GM. It works great, but it REALLY frustrates me. By golly when I say I want 100% throttle, that's what I mean. Not I say I want 100%, the computer calculates current conditions and decides that I should really only get 87% throttle. Pretty irritating when you're trying to pull a stuck truck out in 4 Hi and it won't hardly break a tire loose because of all the computer's calculations. Yes, a tune would fix this...but so would a cable. Servos belong on rc airplanes, not my damn throttle body.
That said, I know of two guys with DBW boats; one works well - and the other is very frustrated with his. So it can obviously work!