I've been asked to sign an NDA at almost every job I have taken in my professional life -- once I have accepted the job -- I have only once encountered a company that wanted me to sign an NDA before the first interview, it caught me off-guard, is this common practice?
I've had to sign NDAs for most interviews I've had. Makes sense considering details about products may come up during conversation. Plus most places I've interviewed at have given me a tour of their facilities during which it's likely I will be able to see what they're working on.