Re: "Internal" and "External"
I'll weigh in on this, but don't expect too much.
As near as I can tell, we are using "internal" in at least 3 different instances that I can detect:
1. The Chinese categorical derivative, which I think has more to do with methodology. All roads lead to Rome, but path X is better.
2. As related to the efficient transfer of power. Internal strength, internal power, etc.
3. As the aikido concept of kokoro, the unification of mind and body. Move from center, etc.
As a general observation, I do not think in any of these definitions, internal is "aiki."
First, all roads lead to Rome. I think the categorical definition of internal and external are not what we want. That is not to say it is unimportant, but look at a good karate person or kung fu person and they will inevitably have some exposure to both. In my opinion, Internal and external movements are both needed in the academic process.
Second, the internal power people are doing something different. I think there is no common language and a lexicon so small it is travel-sized. Right now, the best methodology for sharing the information is physical. It has to be felt is the teaching method because these individuals are still figuring out better terminology and a better method to transmit the information. Dan Harden is doing a seminar in Atlanta in a few weeks and I hope to learn more. I reserve the right to amend what I have said. As of right now, I think what is going on is analogous to the old physics experiment of protecting a raw egg dropped from some height. The trick is to disperse the energy equally against the rounded shell, which is then an incredibly strong shape. I think the IS people use opposing energy to create spherical shapes (expanded energy in all directions) which are then able to absorb force while leaving the insides free to move and unconnected to the force. The thing that hits me most about these guys is you cannot feel where they are; they are not connected to you even though you are touching them.
Finally, the unification of our mind and body. Ikeda sensei calls it body unification. I think this is the aikido version of internal. It works like a geometric proof for circumscribed circles: if two circles are circumscribed with the same center point, a point moving on the circumference of the outer circle has to move faster than a point moving on the circumference of the inner circle. Essentially, moving from your center is the fastest way to move your hand on the outside circumference of that arc.
As I said earlier, I think none of these concepts are "aiki" as we know it. I think they are intended to make your body ready to have someone's center grafted to it.
Hope that doesn't screw things up too badly...