I have seen cumulative turnover BTC of over 600 coins on a single user at Just-dice by the way.
We've taken single bets over 5000 BTC each, with the biggest one being over 7000 BTC.
One guy bet over a million BTC in a single day.
We've cashed out players to the tune of 10,000 BTC in a single withdrawal. We've taken over a billion bets without a single withdrawal problem. We hold coins for over a thousand people who bankroll the site.
It is possible to run a trustworthy, probably fair, provably solvent Bitcoin betting site.