Maybe something like on
Survivor...
First part, ask everyone to answer ten questions in private. They can be about members (which member knows the most about clad coins?), coins (what is the most popular coin at CCF?), or other (what country, other than the USA, are the most CCF memebers from?).
The "correct" answer would be the most popular answer to each question, not necessarily the factual answer; so you might want the questions to be subjective.
Second part is then asking people to answer the ten questions publically. The answer should be what they think everyone else said, not necessarily their own answer.
Keep score. In the event of a tie, there could be a tie-breaker question, like how many people PM'd you with answers, or who was the first person to PM you; the person that guessed the highest on your list would win. or you could go with "first to post the most correct answers" wins.
There is also the option to keep the second part private as well, to prevent copying.
