first of all Dr. Simon is right, never sign an indefinite NDA. Always make sure there is a way for the NDA to end. This applies to any contract you sing, make sure there is a way for it to end. In terms of signing an nda, it really depends on the topic covered by the NDA. Besides the length of time the NDA is in effect for one more thing to consider is the breadth of the NDA. What information that you can and cannot disclose is really important and when signing one it is critical that you make sure that only information pertinent to the product in question is protected by the NDA. If the NDA is too far reaching then the other party signing the NDA could come after you legally even though you thought you didnt do anything wrong.