> On Quora, you can follow not only people, but topics and questions. It defines the world by your interests, not just the people you may know or admire. This is a powerful concept and is not limited to Quora (both Twitter and Facebook also want to own the interest graph), but Quora is designed from the ground up to expose and help you explore your interests.

So, like sub-reddits? A lot of people compare Quora to StackOverflow and derivatives, but I see more of a resemblance to reddit, if you keep only self-posts.