Does anyone know how long the shimano XT disk brakes take to break in?

There isnt a real set time, You should just go riding and just hold them on the entire time, you will get tired quickly but it works. Mayb two rides and it will be worn in?

find biggggg hill...just roll down it with the brakes held :D problem solved.

Most brake manufacturers seem to recommend about 30 stops before the pads become bedded and you get full stopping power out of them. I find that to be more or less correct. My avids took about that long, though that amounted to maybe 2-3 rides at most.

BIGGGGGGGGGGGGG Hill!!! Like TRD said... thats what i did :)

Again, I just go down a big hill with brakes on the whole way. Does the trick.