Snappy, smooth shifting in all conditions. I just replaced my XT 780 shadow with this XT 786 Shadow Plus so that I could get my hands on the new clutch system. Its unbelievable. I didn't think Shimano could out-do the original Shadow design. It was great, but it still that flaw that has haunted all rear derailleurs: too little tention when you're running small to small (i.e. 24t front / 11 rear) in a tech downhill so you always had to shift up to 32t front. No more. I rode super tech downhills in 24t / 11t and never derailled. Unbelievable. Not only that, the shifting is snappier than I have ever seen it. It is great without the clutch, but really that is just the XT780. Flip on the clutch and its like you have a ferrari with paddle shifters.
Oh, and on a side note, the derailleur tuned up extremely easily in my living room - no more difficult than any other XT derailleur and no extra steps. The only "extra" thing to do is flip the clutch switch to engage it. I haven't messed with the clutch rate (I hear a 1/4 turn is a major change), but the stock setting is perfect so far. I'll probably change it up and down just to check it out.
Definitely a must buy. Never thought I would say this but Shadow Plus blows away the XT 780 regular Shadow.