It seems to boil down to having to trust your employer to be honest to their word (and implications) about stock options and what their value really is. Even in the most trusted of environments, I still would not fully trust what comes out of the mouth of the person I'm interviewing with since they cannot speak on behalf of any outside investors, (other) founders, or anyone else with a stake in the company.

Given the nature of 99.9% of employer/employee relations, especially in salary negotiation, I would never personally place any value in stock options of any sort. There is simply no verifiable way to calculate what they are worth with a million different ways for them to become worthless and no accountability for a company to be entirely forthcoming.