FYI, I believe interview questions are covered under the NDA, so if you did interview (and presumably had to sign an NDA at the time) you shouldn't actually be talking about the questions you were asked.
Edit: For the record, I really dislike NDAs on interview processes. I signed one when I went for my on-site with Bloomberg a little while back. I would've loved to talk about the process without using vague generalizations, as I think they hit on effectively every bad interviewing technique out there, but alas I can't. I believe they do little to actually help make the hiring process better.
*EDIT: added last sentence.
If people cannot talk about their interview experiences, there's no opportunity for employers to receive censure for bad interview practices.
Besides, an interview is not the SATs. If this really is the logic for the interview process, then Google interviews are even more broken than I thought.
For your third point, I don't understand what you're getting at. What logic are you referring to that is broken?
In fact, it was so bad I later got a written apology for what happened.
It would be quite a stretch to interpret this as meaning that the questions asked as a part of the interview, or Google's process itself, is "confidential".
At the rate Google interviews, it'd be quite an effort to make sure that no candidate shared information about their interview questions, the format, etc.
Also, this type of agreement during the hiring process is pretty standard for medium-to-large size companies.
As far as I've heard from anyone here, that's the interpretation. Questions are not to be shared, otherwise we'd spend all our time generating new interview questions and never actually getting any work done.
The NDA covers information, not experience.