Steve Jobs: "Picasso had a saying, 'Good artists copy, great artists steal.' We have always been shameless about stealing great ideas."
To steal is to make it your own, to so thoroughly understand it that you can move it forward as if it was always yours. To copy is to simply have it for today without having the understanding it takes to have had the idea in the first place, and so you can't go forward.
http://gizmodo.com/5727913/the-love-affair-between-steve-job...