Matt Straz of Namely.com wrote an interesting article on why not to join a start up.
Taken from the article :
America is a startup nation. Whether it has been manufacturing, whaling or software, one of this country’s defining characteristics seems to be taking unnecessary risks to create markets where none existed previously. As an entrepreneur, I'm a huge fan of startups. Both my parents started their own small businesses, so entrepreneurialism runs in my family. So it may be surprising to know that I don't always encourage people to take the same path. Here's why:
You probably won't get rich. Unless you are one of the founders, the stock options you are granted in a tech startup likely won’t make you independently wealthy. Only a small percentage of startup employees make huge amounts of money when a company is sold. The only exception is if you happen to join the next Google or Facebook — but with thousands of companies started each year, that’s a bit like winning the lottery.
Still, most startups today can afford to pay competitive salaries and benefits. While the upside may ultimately be limited, joining a new company isn’t a vow of poverty.