How Google Reader died — and why the web misses it more than ever - The Verge

One feature took off immediately, for power users and casual readers alike: a simple sharing system that let users subscribe to see someone else’s starred items or share their collection of subscriptions with other people. The Reader team eventually built comments, a Share With Note feature, and more. All this now seems trite and obvious, of course, but at the time, a built-in way to see what your friends liked was novel and powerful. Reader was prescient.