I sized these down quite a bit. 8.5 from my normal 11.5 (I have about average foot width). I based the size decision on shoe fits from other Sportivas with the same last, then went a 1/2 size smaller because they are slippers. They did stretch some during break in but not nearly as much as I had thought and are basically uncomfortable to the point I have to take them off every half an hour and can't toe hook anything. So for sizing, I'd recommend 2 sizes down as opposed to the three I went with.
Now for the other stuff... These shoes are awesome. I cry because I don't wear them much any more. The sole is soft and flexible, forcing decent footwork. You can really feel the hold your stepping on- my favorite part of the shoe. The heel cup keeps your heel sucked in and is amazing for heelhooks. They smear really well and do edges just fine in my opinion once you get a stronger foot from the flexible soles. The toe is basically an amazing rubber spike you can stab in to anything. They do turn your feet orange but who cares, anything unlined is going to dye your feet. So overall an amazing slipper that stretches about a half size maybe a little more, but you won't get a whole size of stretching out of it. I'd buy them again for sure in 9.5, the only reason I haven't yet is the $$$.