Same with kettle-balls.... if someone knows how to use jin/kokyu, they're going to use the kettleballs in that specific way, not in the way a normal strength-and-conditioning person is going to use the kettleballs.
Well I'll put my butt on the line on this one...
I've been training kettlebells for about six months now, and while I agree with Mike that they in no way indicate internal martial art practice (if one were to do that one might consider training an internal martial art...) there are some interesting principles at work that might be worth a good debate.
So here goes....
Weight through heels - we tend to keep our weight back and in the heels.
Legs and hips drive the movement - any of the standard kettlebell movements (swings, cleans, snatches) are solely powered by the legs and hips. My kettlebell instructor is forever yelling at me to "stop using your arms" or "let your legs do the work"
"Reverse" Breathing - We do a ton of it to stabilise the torso and help drive the movement.
So that's just a few thoughts. That being said, like anything (look on youtube, for example) there are tons of examples of how not to do it that are super-muscley, with people using way too much weight etc...
Any thoughts on how these principles might apply to aikido practice or where lifting in this fashion diverges and contraindicates IMA practice?