When I was interviewing last year, I cut off an interview loop with a company primarily because I don't reside in California and their NDA was, "Anything you say, anything we say, forever." Since I was also interviewing with one of their direct competitors that I really preferred, I didn't want to put myself anywhere near a legal situation where they might try to mess things up for my career. They freaked out when I…
The thing you have to realize about commercial contracts is that the law doesn't enforce itself, people who violate them usually don't get caught, etc.
Note also there are other inputs to NDAs. I worked for a firm that did a project for a big accounting firm that itself had confidentiality requirements to its customers so it is natural as an employee of the first firm I help the second firm keep its commitments.
I'd say there are two threads in NDAs: one of them is threats against those who violate confidentiality, another is a description of the procedures that are supposed to be used to protect confidential information. The last time I was doing a lot of consulting I had an NDA that had no threats but lots of guidelines.