A captcha (an acronym for "completely automated public Turing test to tell
 computers and humans apart") is a type of challenge-response test used in
 computing to determine whether or not the user is human. The term was coined
 in 2000 by Luis von Ahn, Manuel Blum, and Nicholas J. Hopper of Carnegie Mellon
 University, and John Langford of IBM. A common type of captcha requires that
 the user type the letters of a distorted and/or obscured sequence of letters or
 digits that appears on the screen.
(from [http://en.wikipedia.org/wiki/Captcha captcha in wikipedia])

Captcha is the one of the most effective spam countermeasures and is gaining more and more ground.  Yet there are problems with the currently only popular distorted letters captchas:  

* accessibility for blind users
* new OCR techniques

The same wikipedia article observes:
 Other kinds of challenges, such as those that require understanding the meaning
 of some text (e.g., a logic puzzle, trivia question, or instructions on how to
 create a password) can also be used as a Captcha.

When the problems with visual captchas are becoming more and more evident, this theoretical possibility is being adopted by more and more web site programmers. But I believe there are more benefits for using it than just avoiding the accessibility problems:
* it can used for email - you would publish your email address together with instructions how to get through your email filters (this would not work agains people selling your address together with the solution of the captcha, but at least should prevent automated harvesters)
* the quiz can be designed as not only filtering out bots, but undesirable people also, this might be usefull for running email lists for professionals who should present some minimum knowlege before being authorised to speak
* the above point should be especially effective for chatrooms - it would be very natural to have a gate keeper for your room

What we need is a good name for this.  Perhaps 'Simple Questions' (from the slashdot thread below) can be it?
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Links:
* [http://www.syndic8.com/%7Ejeff/blog/index.php?p=103 WordPress Comment Verification (With Source Code)]
* [http://it.slashdot.org/comments.pl?sid=159966&threshold=-1&commentsort=0&tid=172&tid=95&mode=nested&pid=13391857 discussion thread on slashdot]