Though it is believed that progressive jackpots have an edge over other games, and give players a good chance of winning, it is yet to be proved that this belief is true. The house edge in all casino games is based on a fixed payout, so if a casino game has a 5% house edge it means that the inconsistency between the actual odds of an event happening, as opposed to the odds they are placing before you, is 5% in their favor. If a casino is aware that an event will happen one in 5 times, they can offer you 3 to 1, on the wager and know pretty well that they will come out ahead.
As you know the casino does not set the progressive jackpot, rather a percentage of each wager placed contributes to its enormous size. This is in effect means, that if the jackpot is not hit by any player for a while, it can reach awesome levels that would award a player better chances, than the odds of hitting it. In other words, it can be 100,000 to 1, against you hitting the jackpot, however if there is $1m in the jackpot pool, the odds are not only in your favor, they could also help you to overcome the negative expectation of all the other wagers in the game.
Progressives are undoubtedly attractive as the payouts are too enticing to miss out! Progressives are linked to a network of casinos, and that is the reason why there is no limit to the expected amount that a progressive can payout. There is however no real way to know how big the jackpot has to be for this to happen, unless the casino informs you, or you have done exhaustive calculations. All said and done, a game with a jackpot in the millions or even thousands, has a greater chance of being a positive expectation game, over any other casino game.