When I came to Aikido, my karate experience helped me, well, not at all. I had a _very_ basic understanding of ukemi, and was like "wow... how's he doin that?"
Come to think of it, I'm still like that
We had a student come to the dojo whose father taught Shotokan. He was I believe a nidan and picked up Aikido faster than anyone I've ever seen. This included ukemi, posture, center and all the rest. Maybe it was because he was so close to it, maybe he was a fluke or maybe they did something different from other schools. I don't really know. All I know is he picked Aikido up damn fast.
With my karate background, I have some notion of how to have power behind my attacks without being too off-balance. I have a feeling of what is open in my body during a certain movement and can react when these openings are taken. I have some knowledge of how my body moves and can move. I can use the same basic principles of deriving power through my body as I did in karate in aikido.
I'm curious Jun. Did your Karate time focus more on principles (ie fundamentals) or was it orientated elsewhere? It seems to me that all the arts would have certain things in common (we all have 2 legs, arms and that getting hit is usually not a good thing) and I'd imagine that focusing on those things would accelerate the learning process between styles.