There are some questions your interviewer has no business asking, and this is one.  But while you may feel like answering, "none of your business, "  naturally you can't. Some interviewers ask this question on the chance you admit to something, but if not, at least they'll see how you think on your  feet. 

Some unprepared candidates, flustered by this question,  unburden themselves of guilt from their personal life or career, perhaps expressing regrets regarding a parent, spouse, child  etc. All such answers can be disastrous.

BEST ANSWER:  As with faults and weaknesses,  never confess a regret.  But don't seem as if you're stonewalling either.

Best strategy:  Say you harbor no regrets, then add a principle or habit you practice regularly for healthy human relations.

Example:  Pause for reflection, as if the question never occurred to you.   Then say, "You know, I really can't think of anything."  (Pause again, then add): "I would add that as a general management principle, I've found that the best way to avoid regrets is to avoid causing them in the first place.  I practice one habit that helps me a great deal in this regard.  At the end of each day, I mentally review the day's events and conversations to take a second look at the people and developments I'm involved with and do a doublecheck of what they're likely to be feeling.  Sometimes I'll see things that do need more follow-up, whether a pat on the back, or maybe a five minute chat in someone's office to make sure we're clear on things.whatever."

A boxing conversion permits any value-type to be implicitly converted to the type object or to any
interface-type implemented by the value-type. Boxing a value of a value-type consists of allocating an object instance and copying the value-type
value into that instance.

For example any value-type H, the boxing class would be declared as follows:

class vBox
{
  H value;
  H_Box(H h)
  {
   value = h;
  }
}

Boxing of a value v of type H now consists of executing the expression new H_Box(v), and returning the
resulting instance as a value of type object.
Thus, the statements
int i = 12;
object box = i;

conceptually correspond to
int i = 12;
object box = new int_Box(i);

Boxing classes like H_Box and int_Box above don't actually exist and the dynamic type of a boxed value
isn't actually a class type. Instead, a boxed value of type G has the dynamic type G, and a dynamic type check using the is operator can simply reference type G.

For example,

int i = 12;
object box = i;
if (box is int)
{
  Console.Write("Box contains an int");
}

will output the string  Box contains an int on the console.

A boxing conversion implies making a copy of the value being boxed. This is different from a conversion
of a reference-type to type object, in which the value continues to reference the same instance and
simply is regarded as the less derived type object.

For example, given the declaration

struct Point
{
  public int x, y;
  public Point(int x, int y)
  {
    this.x = x;
    this.y = y;
  }
}

the following statements
Point p = new Point(10, 10);
object box = p;
p.x = 20;
Console.Write(((Point)box).x);
will output the value 10 on the console because the implicit boxing operation that occurs in the
assignment of p to box causes the value of p to be copied. Had Point instead been declared a class, the
value 20 would be output because p and box would reference the same instance.

Here's what the resume advice company Resume Edge recommends as a sample answer to the question, "Where do you see yourself in ten years?"

In ten years, I endeavor to have refined my strategic and client relations skills. I intend to be a leading expert in estate planning. After having proven myself as a senior manager, I hope to help shape the strategic direction of estate planning services. I could do this in any number of official roles. The important thing is that I will continue contributing my abilities in a challenging and rewarding environment.

• While it is not usually a good idea to try to be a Jim Carey in an interview, depending on how things have gone and who you are dealing with, you might inject a little humour here and ask: "When do you expect to be promoted?" ....or "When are you moving on?... This could easily break the ice. Seriously, you can easily respond that you have no idea as you have no idea what you are capable of so far, although you know it is a lot. Therefore, you want to make sure you are open and flexible to whatever opportunites present themselves. If you actually know what you want to be when you grow up, you could offer to conduct a seminar on how to actuate that.

• You know when you come to that common situation where someone asks you "Where do you see yourself in five years?" Yea you should call a person on that because that question is silly! You have no idea where you'll be in five years nor should you worry. I mean how depressing can that question actually be? If someone asked me that question five years ago I wouldn't have predicted my life to be like this nor would I have wanted to say my life would be like this, I'm not saying I'm unhappy with my life necessarily its just that in a span of five years a persons likes and dislikes change, the people around them either disappear, reappear, or show up for the first time. The things you once loved could become something you hate or vice versa. Aspirations change and feelings lose their magic. Yes you can say what you'd like to see happen in five years but I'm pretty sure it won't and five years from now when you look back on yourself answering that question you'll probably no longer want the same things. There's always hope but no definite so all you can do is live life like you have those five years to look back on...

• When an interviewer asks this question, they're asking where you see yourself within a company. They don't want to hear you say, "Well, in five years, I will be married to a handsome European man, touring the South Pacific in our yacht with a maitai in my hand." They want something like, "Well, that will depend on my individual performance and on the opportunities I'm presented with, but ideally, I will be..." Even if you're going, "Yeah, like I'll be here in 5 years..." act like you will be. They don't want to hear you saying you'll essentially use them to get where you want, and the minute the opportunity is presented jump ship.
• Some might think that you should not tell the interviewer that you want to move up the ladder of success, because they will fear that you might replace them or move on to another job. However, most would recommend that you answer with just the opposite: that you do want to be successful. A good manager wants his employees to be successful and grow in their careers because that benefits the whole company. If they don't want this, you don't want to work for them. As for the actual standards of success and specific career paths, they are very different for different people and different industries. It is most important to show that you do want to be successful.
• Think educationally-- higher degree? certification? Think leadership-- at least one step up from where you are at now.

This is a very common job interview question. Think carefully about your plans. Really answer it for yourself, Where do you see yourself in five years? Where do you hope to be?

The interviewer is looking to find out a few things with this question. First, are you the type of person who plans ahead and sets goals? You should be. Second, do your goals match those of the company and the position? Your goals need to fit the career path for the job. They don't want to lose you in a year or two.