I've been away from the forum for some time, but I'll have to say that my anti-knife comments stirred up much more of a hornets nest than I ever expected.
I'll moderate my anti-knife sentiments (in the climbing arena) by saying the following. It is more about what is between the two ears of the person with the knife than having or not having a knife. A knife is a tool, and a darn useful one at that.
My experiences involve a partner who was far too eager and excited about having his knife along and handy when we went climbing. This fellow has been reliable on many other situations mind you, but has a tendency towards an overly gung-ho attitude. Warning signs were there up front.
I had led a pitch and he had some trouble following but joins me at the belay before long. I ask about one of the nuts that should go back on the rack. "Oh, I couldn't get it out, that was the trouble down there". We finished the climb, but I was annoyed about missing a couple of nuts on my rack, so went back a week later with someone else. This place was fairly remote, but a nice excuse for a hike. The nuts were there and easily removed. On the nuts were hanging the slings -- cut with a knife! The rascal had climbed above the piece without unclipping or removing it (or something) and rather than downclimb and clean it, just reached down and cut the slings.
Needless to say, I never really trusted this fellow again, though we continued to be friends. And I never told him that I had discovered his lie either.
It was a little bit of secret knowledge that I felt was best kept to myself as a sort of landmark in my mind about this guys character. I am sure many of you will have doubts about how I handled this (though my climbing days with this fellow were certainly over).
So there, now you know where I am coming from. A story nobody has even been told before. What is the lesson? Choose your partners carefully, and perhaps beware of those who think their knife is their most important piece of climbing gear.
As for the Spyderco Rock-Jumper, it doesn't deserve any bad press because of this man's questionable knife "handling". But this experience has certainly biased my thinking about knives and climbing.