rtfColorado wrote a review of La Sportiva Karakorum Mountaineering Boot - Men's on October 27, 2011
I'll start out by saying I have owned many pairs of La Sportiva boots and love them (but, unfortunately, I only get a couple hundred miles out of each one, so they get replaced every couple years). I've had the now-discontinued Glacier EVOs for the past few years, and the LS people told me the Karakorum boot was most comparable. I am now boxing up the third pair I have bought from this site and I'm giving up.
The first pair of boots (a size 45.5) I sent back because they were a little snug, but more importantly, because the rubber stuff on the side of the boot was delaminating right out of the box. I decided to go with a size 46 for the replacement. I didn't see anything defective per se, but this boot was noticeably smaller than the 45.5 -- my toes actually jammed into the front of the "bigger boot" but not the smaller.
Soo, I decided I'd take a shot at the 46.5s -- since the sizing just seemed like guesswork anyway. The fit was perfect; the product was not. The left boot was fine: placed on a flat surface it sits flat and is stable. The right boot does not -- it tips significantly towards the left front of the boot which creates a very awkward rocking motion that would be a knee killer on a long backpacking trip (and probably on a short hike for that matter). It also makes for a very odd feeling given the contrast with how the left boot feels. The tread itself looks fine -- there is no noticeable tread missing and no wear, so assume the problem must be with how the boot was attached to the sole, but who knows.
One thing for sure, I do not think La Sportiva is manufacturing a product that can reliably be bought on-line these days, because you have to inspect every boot for defects and because the sizing is so unreliable.