What about a game where you put in 0.1 BTC and guess a number and once a day a random 2 digit number is drawn. Any day there is no winner the pot rolls over. Some harmless fun and perhaps a way to get people using Bitcoins. (The 2 digit number - at least at first - ensures frequent winners)
2 digit number.. so i take it maximum of 99 possibilities.. well that makes the jackpot under 10BTC otherwise everyone will put in 0.1 to every number to guarantee a win everytime.