Netflix
Upon completing the my work at Charles Schwab, I joined Netflix soon after. The challenge at the time was to help the user experience evolve from its premative form.
Adding not just new graphics but new layouts as well so that the effort of browsing movies was easy and satisfying.
One powerful discovery at the time involved natural lifecycle of retention. How the amount of movies watched had a very clear relationship with how long they stay a member. Thus, most design involved encouraging users to watch and watch more!