Comfortable but quality is questionable
I purchased these boots for use hiking and backpacking in Colorado, on and off trail. I tend to hike 5-15 miles per day and usually carry a 20 Lb pack dayhiking and 50+Lbs backpacking. I have a narrow foot and have had good luck with the fit of LaSportiva boots in the past. I like a stiff leather boot with lots of ankle support and the Karakorum fit the bill. I tried them on and they fit my foot very well right out of the box. They did not require much break-in time and are very comfortable. I did add a pair of Superfeet insoles.
I wore these boots on 20 to 30 hikes over a period of 2 months, mostly on-trail in dry, rocky terrain with distances ranging from 5-15 miles. Other than some occasional numbness of my toes from pressure on the top of my feet, the boots felt great and I never got a blister or hot spot. The numbness was always corrected by adjusting the laces. They seemed to be fairly waterproof. I spent one entire day slogging through deep mud on a particularly sloppy trail and my feet stayed dry. The leather stayed looking new after many days of traveling over rocky trail and a few days spent scrambling through talus and scree.
My only complaint with the boots is the build quality. Within the first few weeks of use, the rubber scree protector began to detach from the leather on both boots. By the end of the second month, the sole began to come unglued from the heel area of one boot. I would expect good quality, expensive hiking boot to stay together longer and I assume that the build quality is to blame. I have used other LaSportiva, Asolo, Lowa, and Kayland boots in similar and more adverse conditions that lasted many seasons. Either the Karakorums are defective, or they simply won't last a season of use.
Overall, I was very happy with the fit, but disappointed with the quality. I did not feel I used these boots heavily enough or in conditions harsh enough to cause the issues I had.