Thinking more on cursed and semi-cursed magic items, here is one book I found inspirational:
The Misenchanted Sword by Lawrence Watt-Evens
The plot is pretty much soldier stumbled across a hermit, who enchants him a magical sword that makes him unbeatable in combat. It has some downsides - he can't get rid of the sword, for one, and it is only undefeatable from when drawn until it kills someone. Then you have to sheath it and pull it back out before you use it again. Oh, and it has limited uses - not a small number, but a finite number of kills.
As books go, it's not the best book ever. But it's a good one, and the ideas in it are top-notch. There are demon-imbued enemy warriors, practical uses for a swordsman who can't lose (he gets pulled aside for special missions, no front line service for this guy), and lots of little details that make it feel like the consequences make sense.
The sword itself is really a lot like the kind of thing I'll hand out. You want it, but then again you kind of don't, but you'll use it, and your character will be different for it. It's not just a better weapon, it's a different experience. That's the kind of thing I am looking for.