Alright, I did a bit more research, and it looks like the American Knife and Tool Institute has some facts:

http://www.akti.org/action/new-york-city-knife-confiscation-case-2010

See especially:

http://www.akti.org/action/call-to-actio...-from-retailers

Let me quote: "What the DA is not telling the public is that his office’s interpretation of a gravity knife is ANY folding knife that can be opened with one hand – no matter how difficult." None of the news articles make this point plain, leading most people (like me) to think that we'd be OK with our folders.

It seems that this is a way for the DA to score some political points for his next election, and most of all get millions of dollars from retailers. I doubt the average policeman on the street is all that concerned about little knives, but it would be advisable to exercise caution lest you be made an example. We can write all the letters we want, but I suspect money talks in this situation, and those million dollar fines talk loud.

Good thing the DA is on the side of the law. He would have done well on the other side, too.
-- Da Bing