What Experience is Necessary?

Hillary Clinton states she has 35 years of experience? A post at Talk Left states that "Experience" may be a political weapon if the campaign were to feature Senator Barack Obama and Senator John McCain. Fox Business reports that only one president in the 20th century possessed business experience: Herbert Hoover-- the same Hoover that presided over the Great Depression.

To what degree is experience necessary for a candidate or is just one characteristic necessary?

How do you define experience? What is included?

Here is a description of the executive experience of each president.This list is somewhat misleading as it focuses on the executive experience, mentioning some elected experience, and ignoring other types of experience e.g. Cabinet positions. Here is another list, but the credibility seems lower. Some thoughts:

Six have no elected experience:
George Washington, Zachery Taylor, Ulysses S. Grant, Herbert Hoover, Dwight D. Eisenhower (Everyone except Hoover possessed military experience)
William Howard Taft (Solicitor General of the U.S., Secretary of War, Governor General of the Philippines)

One Term of Service:
Thomas Jefferson (Governor, not reelected)
Theodore Roosevelt (2 years as Governor of New York before being VP to William McKinley before becoming president)
Abraham Lincoln (2 years in Congress)
Woodrow Wilson (Governor for two year, also President of Princeton)