In my opinion, the worst interview question is "what is your greatest weakness?" The same goes for nigh-identical questions like "what are you bad at?" and "in what areas do you need improvement?". Interviewers can expect three responses: 1) a smooth-talking prospect manages to evade the question with as much finesse as a politician, 2) a desperate prospect offers a half-serious response guaranteed to be palatable ("I'm too willing to work weekends, darn it!"), 3) an honest/naive/confrontational prospect, who may in fact be a better employee than prospects 1 and 2, answers objectively thereby digging his own unemployment grave. In any of these cases, has the question done anyone any good?
The last person you should ask about his or her weaknesses is the person under consideration! It's like asking a person to self-incriminate. In Freakonomics or game theory terms, there is no incentive for answering honestly in such a situation. Answer honestly, and the interviewer, who is the other player in the game, may either 1) use the honest answer to stop considering the prospect altogether for a payoff of about -2000 or 2) accept the honest answer but have a diminished view of the prospect for a payoff of about -250. Lie or answer evasively, and the interviewer may either 1) accept the lie or evasion at face value ("gee, I can work him over the weekend, great!") for a payoff of about 250 or 2) reject the lie or evasion and have a diminished view of the prospect's honesty/self-reflection for a payoff of about -250. Lying or evasion is clearly the way to go!
Bad interviewers, bad!