The only time I was asked that question, I responded with "That's kind of a weird question, don't you think? I mean, it's not really in my interest to answer it honestly." The interviewer agreed, and we chatted about interviewing technique for a little while. He admitted that he only asked to see what people say, and that mine was probably the best answer he'd heard.

Got an offer the next day.

It's ironic that such a vapid and well-known question still reveals useful information about a candidate -- precisely because it is vapid and well-known.

You might have had the offer almost regardless of your answer to that question.

I'm pretty sure you're right.