alanback: I think you have it wrong. What they say is it will progress to a certain amount until someone hits it. If no one does, it will stop progressing once it reaches that amount. Sooner or later someone will get lucky.
Think about it, if they knew when the slot machine would pay out, there'd be something rigged, right?

I haven't been to Las Vegas to gamble in a long time, but the last time I was there the video slot machines were really moving in. A lot of them have four reals. I wasn't able to count how many symbols are on each real, but if it's at least 20, that'd up it to 160,000 combinations. Assuming there's only one way to win the progressive pot, that's 159,999 to 1 against it happening on the next pull. The fallacy that a lot people think is that even if you were to play it 200,000 times in a row and yet not have had a jackpot you start to think the machine is due to payoff because of some mystical law of averages. The odds don't change even if the pay out amount does. I certainly would expect to have hit a jackpot or two by the time I'd play 200,000 times in this example, but that doesn't mean it will happen. Then you're hooked and can't leave the machine because all it needs is one more play. You can feel it. Just ask Fred Flintstone about it. :)

Aren't there some slots that don't have a maximum progressive and continue to go higher until someone hits?