I've found a huge gem called Fury's Eye that doesn't appear to do anything, though it is worth 1000gp. Can anyone tell me what, if anything, its good for?
I think it is used in the multiplayer game. It has no use at all in the single player game. Maybe someone else can tell you how it is used in multiplayer, I've never played multiplayer.
If you have any intentions of playing the multi player game I would go back and rebuy it. I know its a pain carrying it but it will get you into places in the multiplayer game you can't get to without it. If you go here http://www.dsedit.net/mods/index.html
you can download some mods to increase the size of your backpack then carrying it won't bother you as much.
I remember this slithly bu**** for a quest.
you need your first dagger, the eye and the book you get from the stones quest. after that you go at some secret cave in the droog area.
it leads you at some small dungueon with chikens that drops hats and badass weapons.
its been a while but if i get to remember more...
Fury's Eye 
the fury eye... 
Linear Mode
