More details from Koo, via the LinkedIn Blog:
A few months ago, I found myself thinking about my connections and the nature of my LinkedIn network. There was an “aha!” moment where I realized that LinkedIn has a unique characteristic others lack — it is three-dimensional. The first dimension is the actual connection. The second is the implicit grouping of connections that tie the social graph together. Many social networks have these first two dimensions, but what makes LinkedIn’s network special is its third dimension: time.
As I began to add more visual elements to the timeline, I realized that I needed a designer to help me manage the clutter on the visual elements, while at the same time causing an aha moment when you see it scroll. I enlisted the help of my colleague Bruno Medeiros, who took a project that was rough around the edges and turned it into something really elegant and polished. The final product is what you see below.