If I remember what I read, and had a Doctor tell me, Brain Surgeons use obsidian to cut with, it is the sharpest know instrument known to man !
Does that answer your question about sharpness ?
I had a good knife, and like a fool, traded it. One day, I'll get another.
Just check out some of the knappers and pick up a peice of rock there working on, or some of the flakes, and see if you can't get cut ! In a heart beat !!
Of course, if it's used alot or abused in some way, they have to be re-knapped, some what. I learned that from shoot'n a flintlock. This rock will shave off metal, if it is knapped correctly, a store bought knife won't.
By the way, some real nice look'n knives posted above !