How likely are you to recommend us to a friend?
This is the question posed to determine your Net Promoter Score (on my wiki).
I also like to look at this as: How likely are you to seek my help again?
So what does this have to do with leadership? Think about who you've worked with today: How would they rate your performance? Would they like to work with you again? If not, how well are you really doing your job?
How would your family rate you? Friends? Neighbors? Local law enforcement officials? Do they like dealing with you? Would they like to again?
If your professional and personal interactions have more detractors than proponents, what can you do about that?