A previous post on this blog (What would you like to be doing 5 years from now?) suggested that the most successful answers to this question place genuine career knowledge ahead of what might get you through an interview. For that reason, it is probably worth considering that the most successful answers have two main components:
1) Relevance to their audience (company, job, interviewer, etc.)
2) Relevance to the future of the individual's career
A great deal of effort is expended to ensure that our answers are relevant to their audience, particularly the interviewer. Of course the most successful answers do not forget this but they also do not forget the importance of the individual's career.
Understanding a preferred direction for the future of your career offers insight into both areas. With greater insight into what is important to you, what you are good at and what keeps you going, your answer begins to resonate with interviewers for its clarity and depth.
Whether you are interviewing for the role of a chief executive or an administrative assistant, an answer based on your values, talents and goals is arguably the best method of creating a link between this question and your personal success.