What I thought of was the decision fatigue involved with too complicated of a scale. I actually just filled out a Likert scale questionnaire this morning, 5 options, and while I took lots of time to consider my exact level of satisfaction for the first question, by the 10th, I really didn't care (clearly, I have very little stamina..). I just meant to say 'positive' or 'negative' and kept clicking down the same column regardless of the exact level of satisfaction I felt. I think that this must be related to decision-fatigue, which I first read about in an NYT article a few months ago and now see everywhere! Of course, the interesting thing as related to this is how the researchers studied real-world applications to see how salesmen (for example) adjust their list of questions to take advantage of people's ability to make complex decisions for a short time after which they tend to default to 'safe' decisions. Based on those studies, I would expect people to use the full scale for the first few questions and maybe default to 'don't know' for the last part of the questionnaire.