I got my first pair of these a couple weeks ago and have put about 80 miles on them so far. The first real test won't come until I get a long run on them (currently 17 miles is the longest run I've done in them), but so far I like them a lot. They feel a little bulkier and heavier than the Streak (even though they are actually an ounce lighter), but they also feel like they provide more support than the Streak. As much as I love the Streaks, I do get a bit of fatigue in the balls of my feet if I do too much training in them. I think the Streak will still be my racing shoe of choice but if the Mountain Masochist continues to make my feet happy I might give them a try in the Miwok.
If you're looking for a pair of lightweight (10.8 ounces) trail running shoes that will give your foot the support and protection that rugged trails demand I highly recommend checking out the Montrail Mountain Masochist. Best new shoe I've tried out in over a year.