I have a full summer on the new-fangled XT hydraulic dual control shifters. If you can get a set new for $150, do it. I have used BB7s on a road bike and on a mountain bike, and I've also used Juicy 7s and 3s, so I have a basis for comparison.
All these brakes will stop your bike from rolling forward, so the base functionality is there. The Devil, however, is in the details. I find the XT brakes are easier to set up, and require less fiddling to have them work well than the BB7 and Juicy 7. I took them out of the box, installed the rotors, installed the levers on the bars, squeezed each brake lever and tightened the caliper mounting bolts. That's it. The pistons in the XT caliper [and most hydraulic brakes] are self-adjusting, which means that there's no need to dial in pad adjustment. It's the same feel, every ride.
Mechanicals aside, the feel on the XT brakes is excellent - smooth and easy to modulate. Shifting is crisp and clean, and I find it totally intuitive. If I need to tweak cable tension, I can do it while riding. If I need to adjust lever position, I can do it while riding. I should mention that although you can use a standard rear derailleur with this lever, it really shines with Rapid Rise.
One problem I ran into was with the Shimano metallic pads. They stop well, but are unbelievably loud. I didn't have to worry about bears, hikers or horses - they all knew I was coming way before I got to them. I did the usual tricks, like sanding the pads and hosing everything down with rubbing alcohol, but it didn't help. I switched to Fibrax metal pads and the noise is gone - they stop great and are totally silent, even when wet. I wish I could say the same for the BB7 turkey warble. Going to a Fibrax metal pad cut down on the warble a bit, but after 400+ days of riding on that brake, I have come to believe that it's a design issue, and that it won't go away. The warble on my wife's bike is just starting to go away now, but it's been 4 years.
CN: XT hydraulic brakes work very well and are very easy to set up. The dual control shifters work very well for me. I didn't like the Shimano metallic pads, stay with the standard pads.