When my friend first told me about Quora, I had exactly the same feeling. "I have to sign up for this? What kind of world do we live in?" But I eventually did, and since gmail separates the emails they send into the "Social" box, which I never have to pay much attention to, every once and a while I read the email and check out a few questions/answers when one looks interesting. Usually it's worthwhile for the amount of time/effort.