The learning is incredible - esp. if you've never been in a startup before and you don't have a business background.

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.