Although I agree that the many seemingly random interview questions (eg, the manhole cover one), aren't really that useful ... (except, maybe for an industrial designer, and just for that one case).
Once you get past the trivia aspect of many of them, they're intended to be stuff that you do not know the answer to, and so you'll have to describe how you'd go about finding the answer. Or not. Eg:
- make up something plausible and/or try to bullshit your way through. (might be useful for sales & marketing? any other field, don't hire.)
- estimate it based on other information
- explain how you'd get the necessary information to solve the problem
When I've been in charge of the hiring process in the past, I try to do a completely unscheduled 5 to 15 minute telephone interview (just call 'em up, as them if they could give you a couple minutes of time ... not all could, as some were at the job they were planning on leaving) ... just to assess how much I think they're bullshitting on their resumé.
Eg, when we were hiring for a senior PL/SQL programmer, I'd ask them what the parts of a PL/SQL block were. These days, it comes up first thing in Google ... that wasn't the case back in 2003. Most of the people we interviewed might've used Oracle before, they might've written SQL for Oracle ... but if you can't give me a clue that you know what a PL/SQL block looks like, you're not up for a senior PL/SQL programmer job.
And, that being said, my go-to question for any in-person interview is:
Star Wars or Star Trek?
In part, you get to see how they handle a situation where there's no best answer, if they're diplomatic in their answer, or if they think outside of the box (eg, Dr. Who or Firefly are valid answers). Where I currently work (a space physics lab), saying that you've never seen either might be a fail unless you're a foreigner. Saying you don't like either, and explaining why with a good reason would be a pass, though. Geeking out about either one too much might still be a fail (as no one wants to work with that person)