I've never signed up to the site, but find this quite interesting. Does that mean you only consume the content via email or do you click through? Sounds like a massive headache for Quora in the first case.
That being said, the emails are brilliant. I don't know how the content is selected, but almost every time I open one I see something eye-catching enough that I click through.
It's kind of a bummer that they're needing to pivot and find a way to revenue - from a non-business, purely consumer perspective I find the site really enlightening and valuable.