Even if the start-up is a huge success, the chances of you making substantial amounts of money are low, unless you have founder-level equity.
You really need billions of dollars coming into a company before non-founders have a chance to make fuck-you money.
Being the first employee of a startup can be the best thing since sliced bread. You take little risk (compared to the actual owners), yet the reward is usually way better than employee number 100. Who do you think is more likely to get 1) a bumb in pay and 2) a better position first?
Being #1 means you work as hard as the owners but for much less -- often you will end up making less than you'd make elsewhere.
Being an early hire seems to be about trading salary & security for experience running a business. Friends who have joined a startup early have said it's the absolute best way to learn what to do -- and many times, what not to do -- when you're starting your own company.
Of course, YMMV. I've heard from plenty of early hires that don't end up near the business side, and don't get much out of it.
Just go in with your eyes wide open, and don't expect to make any money off the stock options. Figure out what you need to do to get your startup off the ground better. Be flexible in doing whatever necessary as Employee #1.
Had huge learning in 6 years. So although I took a pay cut, and I made 0 on stock - I would recommend it to others.
(putting in my two weeks notice tomorrow to be employee #1)