I know what Mr. Bloch is getting at (see the "Tactical Knives" thread) but asking how much folks have used their knives for defense is not a fair way to judge. As has been said, just because a gun has only been used for target shooting doesn't mean it's not primarily a defensive instrument. I'm pretty scared by anyone who's cut more people than boxes!
My primary carry is always something over 3.5" with a blade-hole. It's there to amuse me and make me feel secure. My Wave does all the "real work." The big folder only comes out for play, practice, and (none so far, thank goodness) emergencies. An emergency might be a defensive situation or it might be a wilderness situation - it's something that the Leatherman can't do well and I don't have a fixed-blade handy for (which would be better, of course). Point is that the day may never come when I'm truly glad I have it, but if that's so, all the better. One thing I won't use this knife for are the day-to-day tasks that would make it less capable of serving in time of need.
Am I being paranoid carrying a knife for "emergencies?" Maybe, but we have enough people in the world who are compleetly unprepared for such things, so even an ounce of preparedness on my part is a step in the right direction. Besides, it's not doing anyone any harm that I carry it, and I enjoy it a lot. Even though I don't use it for day-to-day chores, I do keep in practice with it, and there is a measure of comfort from knowing that it can be in my hand with little more than a thought. When something in the world puts me in "condition yellow," my hand instinctively brushes past the clip, and the knowledge that I'm not completely defenseless lets me evaluate a situation with greater calm and rationality. I think that my chances of panicking and getting myself or someone else hurt would actually be greater without that knowledge.
I don't agree with widely marketing knives based on defensive use or "killer" potential because of all the trouble this has caused the handgun industry. But we should also remember that something is better than nothing, if you have the clarity of mind to use it properly and appropriately. There is a local self-defense instructor who advocates the carry of a large, stiff hat-pin. Same point - it's better than your fingernails for making someone let go, so you can beat feet.
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-Drew Gleason
Little Bear Knives