What is an ‘expert’ really?

Malcolm Gladwell, in his book Outliers, defines an expert as someone who has devoted a minimum of 10,000 hours to becoming skilled in a single narrow field, such as; tax accounting, estate planning, money management, or financial planning, etc. Gladwell’s definition is as good as any and makes sense to me the way he lays it out in his book.
 
How many hours have you devoted to your skill, to your career, to what you really enjoy doing?  When someone tries to tell you how to do your ‘job’ do you have the confidence to share with that that you are the expert in this field and they need to take your advice and do whatever it is you are recommending (said nicely and with confidence)?
 
When you are looking for an expert in a certain field, would it be important to you to know how much time they have invested in their field to be that expert that you are considering hiring?  When someone devotes 10,000 hours of their life to perfecting their skills, I would suggest that they are probably an ‘expert.’ 
What do you think about this?