As cool as that site is, weerwolf, Clay himself will tell you that those moves have nothing to do with knife fighting. I can do aerials with a balisong, and I am also familiar with Filipino knife fighting, and never the twain shall meet.
I've just got to add to the chorus here. Nothing beats training in person on a regular basis. Seminars and camps should be supplements; videos and books little more than food for thought.
Actually prevailing in knife-on-knife combat is an incredible challenge. I've worked on my skills a fair amount, and whenever I spar I am horrified at how cut up I would be. You can spend your whole life pursuing mastery; it recedes into the distance.