I remember how much I hated estimation ... and how my adverse reaction to it came back to life when my stepson was doing estimation at school. I just never (and still can't) grasp the concept of WHY estimate when you can have the correct answer? ... I do understand all the points lucounu mentioned ... but still ...
And I am already seeing the same lack of understanding for estimating in DS4. It's either the correct result or nothing at all for him.