The software development industry is known for its notoriously bad interviewing practices.
The reputation is well deserved.
Few industries put prospective candidates through the arduous, multi-part interview process that even entry-level software positions often require. Few professions demand that experienced practitioners, with a CV stuffed with academic and professional accomplishments, complete humiliating skill tests (usually scatter-shot testing whether the applicant happened to recently bone up on an esoteric area of a barely related niche), often under absurdly unrealistic conditions: It's sadly common for a candidate to be forced to write pages of code with nothing but a pen and paper -- despite the fact that most developer's hands cramp up after the first sentence -- supplying them with none of the normal development resources that they rely upon in the real world (forcing them to unrealistically recall the specific call patterns of seldom-used API functions, which is something that no real developer does in the era of online documentation, rewarding rote memorization while punishing problem solving and intelligence).
Many interviews feature smug "How To Move Mount Fuji" interviewers who are desperately trying to impress the candidate -- or their peers in the room -- by grilling the nervous applicant on whatever niche the interviewer happened to focus on that morning.
This is unfortunate.
While most shops are trying to hire intelligent, adaptable computer scientists, the interview process is often more suitable for the hiring of software technicians, which is perhaps why copy/paste, everything-looks-like-a-nail developers manage to hang on.
Yet for all of the well-founded complaints about industry interview practices, one oft-repeated complaint derives from a misunderstanding of the conversational nature of interviews.
[I'm spurred to write this entry after seeing a number of "idiot interviewer asked me about more than the limitations of a JavaScript closure!" atop the meme sites over the past few days]
Unless you were recruited right out of university, you've probably been asked that question, and you probably complained about it to peers in the real world and online. You have probably read others complain about the same. You've probably heard it and its ilk declared obsolete (and it is true that the backlash has generally sidelined this particular question, though it has been replaced by equally subjective personal questions) .
"I just BSd and said that my weakness was that I work too hard!" is a frequently heard comment about this reviled question.
So why do people hate this question so much?
Usually it comes down to a misunderstanding of the real purpose of the interview.
An interview isn't an objective fact gathering exercise: If the interviewer just wanted to ask what year you went to school and what your GPA was, or whether you'd used the masterpage functionality of ASP.NET 2.0, they'd give you an application or put it on the requirements list -- just like McDonald's would if you wanted to man the fryer -- and be done with it. Many job submission sites, industry wide and organization specific, do exactly that, getting applicants to concisely complete some structured data entry screens, describing exactly which skills they've used and to what level and for how many years, allowing technican style presorting based upon skills.
Instead an interview is a conversation. It's to determine how you think, how you converse, and how you interact, and to have a conversation about technology, prior positions and projects to gain information that can't be learned from a CV.
An interview is often a test to see if you're compatible with the firm. To see how honest and forthright you are on your feet. To test how humble or arrogant you are. To gauge if you have a sense of humor. To learn detailed facts about your prior experiences and exploits.
It's a bit like a first date.
So what is your biggest weakness?
Answering that you work too hard will often get you rejected as a liar, or as someone who is entirely unaware of personal weakness. Answering that you're a perfectionist -- another favored "I'm so clever that I game the system" answer -- again either implies that you're a liar, or worse that you really are a perfectionist (which in this industry means "someone who'll never, ever actually finish anything, always deflecting criticism by proclaiming that they're in the pursuit of perfection").
Giving an arrogant, can't-be-bothered-with-such-inanity response -- or a PC answer that alludes to the same -- could be considered useful in that it'll help the interviewer save themselves the time and trouble of dealing with a prima donna: If you don't have the time or patience to answer such a simple, obvious question, too sure of your pompous self-importance, then it's good that you set the rules for a very short game right away.
How then to answer? Honestly might be a good start.
"But if I answer honestly, the interviewer will pass over me in favor of the smooth-talking guy who claims that his biggest weakness is that he's too loyal!" you might retort.
While it is definitely true that sometimes interviewers are morons who happened into a position by luck, good looks or nepotism, your best bet is to assume that they're reasonable, intelligent, understanding people. Assume that they aren't fooled by applicants who pretend that they're perfection personified, and that they can understand that everyone has weaknesses, unique personalities and unique strengths.
They know that you aren't going to be a perfect worker that knows everything, can do anything, and is infallible.
And if the interviewer is a moron, it's probably in your best interest that they nix you as a candidate anyways (presuming you aren't really desperate): Do you really want to work at a place like that? (On a similar theme, if you really desire a certain percentage of telecommuting time, or you want a private office, or you demand triple-screens, ask for it! You'll either get it, or you'll avoid getting a job or environment that would make you unhappy: Both sides will walk away probably muttering "the nerve!", but in reality it's a Win/win).
Just be honest. Relax, and engage in conversation. If you think that an interview is going to be a walkthrough of your CV or questions about how many gas stations are necessary to serve a population 175,000 city, the vast majority of interviews are going to disappoint you.