For now I gamble with dollars on poker tables, but I started online gambling with bitcoin's, poker and slot games as well. I've even got 1 whole Btc last year on slot games, but since that time I had no luck, so now I almost do not play such kind of games 
No one know in advance that either he will be lucky or not. I think that most of the people play online gambling using bitcoin, which is i think that the easiest way to use. Most of the people convert their money from fiat to bitcoin only for playing gambling.