Some really interesting and intelligent postings on the subject. I have been training JKD since around 1986 and have been involved in waaaaaaay more than my fair share of internet battles over this subject (as well as all the political BS from way back in the Nucleus days). So, instead of trying to take the point away from the intention of the thread, I will say what I have discoverd about my own truth on the subject.
I began JKD wanting to learn everything and anything I could on Bruce Lee. I will admit to the disgruntlement of the mods here, that I love Bruce Lee and Brandon Lee. I feel a very strong connection to the man, his legacy, and all of his teachings. Does that make me a blind worshipper...no. I have loved Bruce since I first heard his name mantioned and saw my first Bruce Lee movie back in 1980. I know, that sounds contrary to what I said about not worshipping blindly at the altar of Bruce, but I also know that Bruce was only 33 years old when he died and hadn't been able to do more research in his short life.
So, I set upon my journey to obtain everything he wrote, or was written about, his life, his art, his movies, everything. For the longest time, I was a proponent of the Concepts way of JKD. I believed that what Inosanto said, was what was to be. I won't go into all the details of the journey I have been on in this regard, but I was personally successful in what I needed and wanted out of my training. Then I met someone who had/has a VERY extensive background in JKD and was a large proponent of the "original" JKD movement.
Once I began to train with him, I began to realize (very quickly) that I was missing a LOT of information on Bruce Lee's art. I was pretty stoked to be learning the things that Bruce Lee actually taught over his lifetime since the day he arrived in America. Not to sound like a "braggart" but I actually started to pick everything up very quickly and absorbed it like a sponge. I was able to meet and train with both Larry Hartsell and Leo Fong. Through them, I began to see the light, so to speak. I was even more convinced that I was doing the right thing and learning the right information. So, up to that point in my life (1995) I was pretty secure in my beliefs and couldn't be happier. Then, I was slapped in the face for the very first time.
So, to summarize my beliefs up to this point, I felt, and to a large degree, still do, that if you claim to know anything about JKD, you should have at least a basic working knowledge of what Bruce actually taught. You don't have to be a scholar on everything "Bruce Lee" but understand the proponents and connecting truths that Bruce made as a core part of his teaching.
Economy of motion
Power-side forward THEORY
That is just a lumped-together category, as you can tell, as others have already touched many of the details. Obviously, those things can and do exist in many arts, not just JKD, but as a rule that is what I feel Bruce Lee wanted to be the core of the art.
For me, JKD is that which works in a street attack (and all the philosophy that you can gleen about life, etc I am not a philosopher so I won't pontificate that point LOL)
Actually, maybe I am oversimplfying myself a bit. Let's say, that I feel that JKD is that which works VERY effectively in a street attack using the above mentioned core compentancies, if you will.