I'm surprised I haven't seen more of this, but I've just ran into two people in the forest within the last half hour that used the item duping glitch to dupe firebombs instead of souls, which, as you can imagine, is rather annoying.  So if you see anyone with a dragon head on, be a bit wary.

It seems that you can dupe the 2handed R2 effect of weapons as well, as was the case of my last fight where the person just kept spamming the slow aura of the stone sword, which also does a bit of damage to you.