I saw on tv once about this guy that wrote a program that could figure out a random number generator's algorithm by punching in numbers that it produces and predicting the next numbers. He went to Atlantic City and won the jackpot on some game.
This only works with pseudo-random generators. In order for this to have worked for a gambling machine, he'd have to have been (a) playing on a really old machine that used pseudo-random numbers, since all of the new ones use proper random algorithms, and (b) be intimately familiar with the inner code and hardware of the game in question, since the output of a pseudo-random generator is very hardware and code dependent. I seem to recall reading something about this in the documents at
http://www.wizardofodds.com , but I don't remember exactly where it was. That's a great site, by the way, if you're interested in information about randomness and probability. I was tempted to consult this guy when we started talking about the car player's shuffle accuracy, but FerretBoy seems to have us covered already.