I really, *really* dislike hearing brain teasers in an interview.
Not because I don't like puzzles (I do), not because it's not a good way to judge the candidate (it is, in a sense), but because it shows up the deficiencies of the interviewer and the company.
Most of the time, the interviewer isn't into puzzles. They just looked something up on the internet, got a list of "here's a puzzle to ask the candidate", and mindlessly ask the question(*).
And when this happens, I answer the puzzle and then ask the interviewer my own puzzle, and see how they react.
Invariably, the answer is "I don't know. What's the answer?" within 3 seconds.
I don't want to work for someone like that, I don't want to work for a *company* that would hire someone like that, life's too short to spend time working amid thinkless drones.
A really bad company is when the VP or someone sticks his head in the door with a "hey, just wanted to see how it's going. Can you answer this question for me?" thing. I keep a chinese block puzzle in my pocket (that I invented) for this exact situation: I write down his answer on the whiteboard, hand him the puzzle, and say "if you can't disassemble this and reassemble it before the day is over, I don't want to work here".
Polite and reasonable interviews don't get this level of response, but turnabout is fair play. Ask me about my experience, ask me to solve a typical problem from the job description, get a feel for how well I work with others... these are reasonable.
But ask me why sewer caps are round, and you'll have to prove why you're company is good enough for me to work there. While you're interviewing me, I'm also interviewing *you*.
If everyone was more aggressively responsive to these types of games, companies wouldn't play them.
(*) Once, just once, I got into a real discussion of puzzles with the interviewer, I've got no problem with that. So long as it's not mindless bingo-card checkmarking, it's OK.