I figured they were used earlier, but haven't done enough research on them.  The pics and diagrams I have of the 16th century one appears to have sort of a peep sight.

poor fellow let us know if it actually launches will you Lol

Here are a couple of stonebow links:

http://www.thebeckoning.com/medieval/stonebow/about-sbow.html
and
http://www.ctmuzzleloaders.com/mlexperiments/bulletbow/bulletbow.html

I have always been very interested in the stone bow has any one actuly fired one

I've shot them.  I have a stone bow (hand bow) that took me about two months to learn the technique for, and a couple of pellet crossbows.  They don't shoot very fast, and look a little, well, silly.  I have only used them against paper targets.

You have a string with a pouch, or a double string with a pouch, for stability.  You put the stone in the pouch, draw the bow, and you sort of twist the bow around as you shoot so as not to hit the bow.  It's also important to have the pouch a little way up from the grip, so that it won't hit your hand by accident.  I've found it better, on the advice of ATARN, to draw the bow twisted - that is, twist the bow to the left before drawing, and try to maintain it as I draw, so that the bow naturally twists when you shoot.  It's quite difficult technique.  I find the handbows better than the crossbow styles, though.

well this is defenitly not going to be a stone bow vs sling
comp.

Man I almost want one for myself. Would cut down on the $$ needed to replace lost or broken ammo.

 
-Unsapien