I would echo some of my earlier comments to Peter's blog and won't repost them here.

From my perspective, balance and structure are not the same concept. Kuzushi, I think, is a concept targeted not towards one's physical (or emotional) balance, but rather their ability to accept and respond to force. I have worked out with some number of good people who can be quite precariously balanced or unbalanced but remain difficult to throw because they are still able to accommodate the forces affecting their body. There are several good judo videos in which you can clearly see a visible displacement of posture/balance but no kuzushi. It's maybe in the breakdown of our ability to manage forces affecting our body that we see kuzushi.

It's in this sense that I think more about my partner as a catalyst for my mismanagement, a role that can be also filled by a child's toy laying on the ground or a raised crack in a sidewalk. All these failures are a breakdown in my ability to manage my body. From this perspective, I am always seeking to remain within my own ability. Much as Messisco sensei says, "my own self" - I just don't happen to be a 6th dan aikidoka training for 50 years. It's also a key distinction between taking ukemi and being thrown. When I take ukemi, I remain in control of my body. When I am throw I lose control of my body. As I am prone to say more often, I think we need to keep our eyes on our own paper more. If I move in balance then it should prove difficult to achieve kuzushi against me. If I move with aiki than I should have impact on forces that come into contact with me.