IANAL, but "duress" wouldn't be the applicable legal doctrine in that sort of case. There is a concept known as "unconscionability" or "unconscionable clauses" that is relevant: http://en.wikipedia.org/wiki/Unconscionable.
The common description is that you can't sign away your rights. A clause that says you can't sue your employer at any time for any reason, even after you quit, is obviously not going to fly with a court of law. That's the common idea, but it seems to go a bit further than that.
The common description is that you can't sign away your rights. A clause that says you can't sue your employer at any time for any reason, even after you quit, is obviously not going to fly with a court of law. That's the common idea, but it seems to go a bit further than that.