Way back when IBM was a big juicy target for lawsuits, an employee told me IBM doesn't sign NDAs: "We don't want you to disclose anything confidential to us." Because, how the hell would they even keep track of the information status across all those people and projects? Not realistic.

In my experience NDAs aren't practical to enforce and hardly anyone takes them seriously. I've seen them used mostly as a sort of social ritual, much like shaking hands, asking "How are you?", and "Hey, can you keep a secret?".