Advance Directives

Filling out an Advance Directive is something I've been meaning to do for awhile now. What exactly is an Advance Directive? I'm going to borrow the definition from Compassion & Choices of Washington because it is succinct and lovely: "Advance directives is a general term for oral or written instructions about future medical care if a person becomes incapable of stating his or her wishes. In these documents, both wanted and unwanted treatment may be specified."
Compassion & Choices offers a form for filling out Advance Directives in Washington state. The form includes instructions and things to consider as you go through each step of the process. If you don't live in Washington, you may still find the instructions and tips useful ... but here is a link to laws by state.
This came into my mind again recently because I have been reading Eleanor Clift's book, Two Weeks of Life. She writes about her husband's death, at home, in hospice care, and contrasts it to the death of Terri Schiavo. (Schiavo died around the same time as Clift's husband.) Now, my mom worked in health care, so I assume my family would not keep me alive on tubes for 15 years, but what if my mother were to pass away before me and others just couldn't make the decision? I guess that people know my wishes, but isn't it my responsibility to put them down in writing? Shouldn't I take charge of communicating those wishes instead of leaving it up to surviving family members to figure it out under already stressful circumstances?
I'm going to be out of town for a wedding later in the week, so I won't be getting to this immediately, but I will definitely write about my experience as I fill out this form. I'm hoping to approach it in the near future.