[vonnik]

NDAs are very difficult to enforce, which makes them almost useless, and which indicates that the people who ask you to sign them don't know what they're doing.

If the investor is a large strategic, an NDA may be a simple formality required by their legal department, which you'll need to sign for them to discuss strategy with you.

If you don't trust someone, you shouldn't share with them information that requires an NDA. If, in addition to that, you fear that a signed agreement would be wrongly leveraged, then I would suggest not doing further business with them.

If you do sign the agreement, then you should try to minimize the legal costs you could incur due to a breach of the agreement. This will probably involve making arbitration the sole legal remedy. These clauses can be added to your contract:

http://pastebin.com/1YardRRu