I've always thought search engines and Q&A sites (this seems to be where the action is these days) could harness the power of quizzing. Google seems to have designed the whole process nicely. Judging by how they have taken the pains to make these questions relative un-google-able via answers to these exact questions elsewhere by people trying to solve them, a lot of thought has gone into the design.
As someone who runs a daily quiz blog himself (and has a similar in-built "show answer" design), I wonder how easily the scalability-conscious Google generates these questions. The questions seem to have a human hand in them, judging by the framing.
There's always place for one more daily quiz site, I guess :-)