What about draw times? what is better? 1 week, 1 day, 1/hour?
I would think a site would have the most success with several formats. Not so many it becomes confusing, but you could start out with each of the ones you listed; hourly, daily, weekly.
Hourly could be smaller pots and payouts, you would probably have to tweak it depending on number of entrants. The daily and weekly could be larger, even if the entry fee is the same or smaller than the hourly as you would have a longer period of time to acquire entry fees, or get more participants.
So maybe say a 0.001 bet would payout 100/1 hour or 0.1 BTC, 1000/1 daily or 1 BTC, and 10,000/1 weekly or 10 BTC. This would be of course assuming you can get enough tickets sold to cover your payouts. I would think this would require a lot of tweaking until you had a stable player base you could make more accurate predictions with.
