There is an excellent Quora thread on this very topic. http://www.quora.com/What-are-some-good-questions-to-ask-yourself-to-determine-if-you-are-ready-to-join-

There is an excellent Quora thread on this very topic. http://www.quora.com/What-are-some-good-questions-to-ask-yourself-to-determine-if-you-are-ready-to-join-a-startup http://www.quora.com/What-are-some-good-questions-to-ask-you... To excerpt a relevant point from the top answer: "I'm not sure if people "become" ready for a startup; in my experience, people are either small-company types or big-company types. When big-company types of people join a startup, they are typically ineffective and (if installed as a manager), a major force in slowing things down. When small-company types of people join a larger company, they tend to become annoyed and dissatisfied, often leaving quickly"