I have always given two weeks notice with any job I have left due to the fact I always remain in the same field, everyone knows everyone so it is always good to be known as a decent guy. One job I worked for, I was there almost 3 years but one day everything just blew up and I was so livid I called my direct supervisor and let him know I quit and was walking out the door, funny thing is anytime the company has been contacted for a reference it was always good.