I am normally somewhat leery of Wikipedia, but the JKD entry was pretty insightful, IMHO. Some good points:
Jeet Kune Do advocates that any practitioner be allowed to interpret techniques for themselves, and change them for their own purposes.
This seems very common sense to me, but I have been surprised that many instructors in some "progressive" arts have a very "traditional" view of proper ways to do techniques.
The (traditional) schools Lee criticized tend to see their initial conservatism as a safety feature; a legacy of practical experience passed down from generation to generation, said to ensure that their students are thoroughly prepared for advanced martial arts training, skipping nothing and developing intangibles such as good character, patience and discipline. The hierarchy of the traditional schools is said by this reasoning to provide a level playing field for all students by instilling respect and care for one's seniors, peers and juniors, so that everyone, not just the physically gifted, has an opportunity to benefit from the training provided in a martial art school.
I think the directness of JKD training (and by extension modern MMA) does NOT provide a level playing field, in the sense of the traditional schools as mentioned in the article. But should it? I realize that as I write this, I'm not sure what my answer is.
I think it's good for instructors to know that there are other guys out there that can have significant skill without much training in a style. It is also good for beginners to not have a false sense of confidence about their skill level.
Wow. Sorry for rambling. This has actually given me a bit to think about, when I thought my position on JKD was fairly settled.
"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin