Magic Items: Powered by Souls (tm)

Here's a quick idea re: magic items. Rather than being powered by Magic Pixie Dust, or gold infusions, or whatever, what if any magic requires the power of an actual soul to fuel it?

Souls could be willingly given, or forcibly bound to an item. For example, I can see noble knights giving themselves to be bound into a magic armor or something. Its like Fantasy Organ Donation ("He's flatlining! Check his shield... Yes, he's a Soul Donor! Quick, get him to the enchanter, stat! We need to get him into that Shield +1 before he flatlines!"). In this event, factions would be very unwilling to sell magic items except to close allies, and they would certainly try to recover lost items. They might have a compact to destroy the item after completion of a task or period of time, as well, so that the sould can be released to its final destination.

Souls could also be forcibly bound. This is obviously fantastic tactics for Evil, Inc. It also gives a great reason for bad guys to capture good guys.

Consumable magic items might just require part of one's essence. Instead of a whole soul, maybe just a healing surge/temporary ability score reduction/etc. Thus while still valuable they are not as sacred.

So, if the PCs want to make a Blade of Orc Slaying, they need to collect their masterwork blade and find a special forge or whatever reagants the GM wants them to get -- but they also need someone who can be bound to the item. Whether that's an orc chieftien or a fallen knight or whatever, it will certainly be an interesting quest.

It also encourages mages to be sketchy. Which is always good for fostering that "rare magic" feeling.