While Ning is sadly adopting the use of CAPTCHA’s (a tool that no longer works thanks to nefarious spam bots and human spammers), as well as email verification (which can land in the spam folder), their “Twilight quizzes” may help thwart spammers (whether virtual or in the flesh).
Adding a quiz to your Ning Network’s sign-up makes it difficult for a spammer (or potential spammer) to join. Why? Because they’d need to take the time to research the answer your question correctly — and that’s the opposite of what they want to do! [...]
Let’s say, for example, I run The Twilight Saga and I want to make sure that every person who joins my Ning Network is a true Twilight fan and not a spammer or troll. I would want to add a question that every new member should know the answer to, like “What is the name of the second Twilight novel?” Capitalization doesn’t matter, so members can answer “New Moon” or “new moon” and either would be enough to prove that they’re a real person who loves Twilight. (Official Ning Blog)
Since most human spammers are (to put it bluntly) lazy, evil beings seeking a quantity of comments (as opposed to creating a quality comment), they will probably skip over any blog requiring a quiz and instead look for a blog with less defenses.
Note: Self hosting WordPress guru’s can install the Quiz plugin which will provide a similar effect upon their blogs. If anyone knows of a similar solution for MovableType or Blogger fans, feel free to inform the rest of us below.