Let's get real about something: they're business guys, and you're the technical muscle, right? You seem young, and you're probably as good at sizing them up (note your "great people" comment) as the average MBA is at writing code; by this, I mean, not at all. Don't even try. Make your decisions based on hard facts, such as how much equity you have already and when you will start collecting a salary, and not based on "warm fuzzy" feelings of loyalty or how much you will get "when times change". Unless you're seasoned and have been in the business world for a decade or so, you are way out of your depth when trying to size such people and their promises up. (Of course you like them! Their job is to make people like them. They probably like you, but do they respect you?) Business people over-promise because the worst of them are sociopaths and the best of them have great intentions and are wonderful people but still are ridiculously overconfident, just because they have to be in order to succeed in that world.

They may be great guys, but you really need to get a firm commitment regarding equity. You're taking a risk and have a right to know what the rewards will be. A promise, especially a subjective one, means nothing. What does a "big" share even mean? If the company is valued at $2 million and you get 0.25%, that's a $5000 bonus, which can be described as "big" but is quite lousy in comparison to what you actually deserve. Remember that the business guys, due to the overconfidence that is characteristic of that sort, would still consider such a grant very generous. After all, it's going to be a $10 billion company one day, and that 0.25% is going to make you a millionaire many times over, no?

You're taking as much risk as they are, and you actually have the technical skills. You deserve a better deal. If your leaving would hurt them as much as you think it would, then they will give you equity, and they'll actually respect you more now that you're not letting them take advantage of you. Or, they might let you go, in which case you're better off to have this happen sooner rather than later, after having wasted even more time.