I had a somewhat odd experience with this.
About 8 months ago, VIP informed me out of the blue that they were giving me a $500 casino bonus with a considerable rollover (~20x ??).
With no expectation of having anything left after the rollover, I started playing blackjack and actually ended up turning it into around $900.
I describe it as odd because I have played a lot of blackjack at live tables - so I know how you can have your little hot streaks but if you're not a proficient card-counter, the money gets pissed away in the long run - even if you play flawless basic startegy. Well as I was working through this rollover at VIP, it was like things were actually rigged in my favor.
I have no explanation for this but that's how it seemed. I kept getting good cards in a way that seemed unnatural.
Anyway, I completed the rollover and pulled out all the money and have never played at an on-line casino before or since. So I am a lifetime winner at on-line blackjack.
From what I have heard, I wouldn't recommend it to anyone though. As I say, it really felt like something unnatural was going on. (Like they were trying to get me hooked or something?) I don't know. But I wouldn't recommend it.