I think part of the attraction of hydraulic is the near-perfect sensitivity between what the rider does to the brake lever and what the pads do to the disc. Perhaps the sealed nature of the system is an advantage in some ways too.
Having said that, I've stopped allowing my XT front hydraulic disc any excuses. It's broken in, it's bled, it has good modulation and sensitivity, but it's just not that powerful. Guess I was expecting the kind of grip I've seen with Hayes hydraulics in the past...
Not trying to start a Hayes-versus-Shimano war here, so I hope no one takes my criticism of my own brake the wrong way. But if the only advantage I'm getting out of my XT is sensitivity, and not extra power, then I'm a bit disappointed, particularly after building a very beefy front wheel for this thing, and converting to separate shifter pods too. Heh, maybe I should try some non-Shimano pads in it before I give up... any suggestions?