One way to deal with Validating Questions would be to automatically allow questions that match an approved list of formats. To add to or amend the list of formats you'd circulate a proposed definition and allow other proposals to be added, then let people meeting some criteria (eg users with more than X bitcoins in escrow on currently outstanding bets) to vote the different definitions up or down over a 7 day period.
So, for example, one format might be: {DOW_JONES} on {FUTURE_DAY} will match {PRICE_RANGE}
Where, for example, {DOW_JONES} for a particular {FUTURE_DAY} is defined as the closing price of the Dow Jones Industrial Average, as retrieved at noon on the day after {FUTURE_DAY} by looking at a list of 5 URLs such as:
https://www.google.com/finance/historical?cid=983582&startdate=Dec+25%2C+2012&enddate=Dec+26%2C+2012
parsing each one via a supplied perl regexp or similar to get just a single number, and then taking the median value of that number.
In effect, the bet would be actually about values on a number of different web pages, rather than about the Dow Jones index itself, and the people placing the bets would be assuming the risk that the web pages on the resolution day didn't reflect the actual stockmarket price they expected it to.
This greatly limits the kind of questions that can be asked.
Intrade, the prediction market website, has shutdown. According to their website:
With sincere regret we must inform you that due to circumstances recently discovered we must immediately cease trading activity on www.intrade.com.
These circumstances require immediate further investigation, and may include financial irregularities which in accordance with Irish law oblige the directors to take the following actions:
During the upcoming weeks, we will investigate these circumstances further and determine the necessary course of action.
Here's a link to an article on the slashdot website with more information about it:
http://slashdot.org/topic/bi/intrade-shuts-down-under-murky-circumstances/
Has anyone looked into the feasibility of creating an open source version of something similar, using a distributed application and a microcurrency (such as bitcoin), that couldn't be shutdown?