Ask HN: How much non-disclosure agreements limit you in the future?

I am a programmer who is thinking about getting involved with a certain early stage startup. For our meeting I am required to sign a non-disclosure agreement, which is I'm guessing a standard procedure. I have no problem with it, as I have no intention of stealing their idea. However, I noticed there is no time expiration on the contract. Does this mean that by signing this I would never be able to work for a different similar company, or do my own related thing?