That's presuming that the price at Mt. Gox is "the market price". As we've seen, prices there may vary from those at other exchanges, by as much as 2 to 3 percent, consistently.
I'm looking at entering into a financial agreement with someone that will be denominated in USD but periodically settled in BTC equivalent. Is there anywhere online where one can look up historical Bitcoin data for a specific date and time?
E.g. what was the price of bitcoin at 12 noon on August 4?
Any suggestions on how to word this or structure it into the contract?
If it doesn't matter what time of day, then just so that it is consistent and widely available, you might want to specify that the price used is the closing price at the end of the day (UTC). If the contract is short term (under a year), the Mt. Gox BTC/USD market will probably still have plurality over other markets but just to cover the bases, the language might want to say something like the closing price from the BTC/USD market with the largest volume on that day.