I noticed before that someone was wondering where some of the keys he has go, and as I was wandering around Grimhold just now, I noticed something.
I had the key to the room with the locket, but as I was fighting goblins, one of them went past that door and opened it (I saw him do it, and when the goblins were all dead and I went into the room, the locket was in the dresser).
I've seen goblins and other NPCs open doors before, but this was the first one that I knew (well, when I found the locket I knew) that I had a key for, which was now useless.
I'm sure you didn't mean for NPCs to open locked doors, but you might look into it as a fix for the next patch. At least if locked doors stay locked till the player unlocks them, it will cut out some of the backtracking and hair pulling looking for places to use keys. It still won't help if the player picked the lock because he didn't have the key with him at the time, but you can't fix that.
On another note, is there any way you could consider allowing the player to get some info on items you right-click on to use before using it (say a popup window describing the potion or spell scroll and asking if you want to use it)? Perhaps for the Gold Edition and/or Eschelon Book 2.