My biggest bet using bitcoin was around 0.005 BTC. I won it from a contest i participated. The requirement was to wager it up to the minimum withdrawal amount. That time the minimum withdrawal amount was 0.001. The painful part is I lost the bet and everything was gone. Aside from that bet, the next time i bet on bitcoin was $10 of BTC. This time I deposited almost $50 used some on casino game and the other $10 of btc on sports betting.