Like he says, academically, there isnt much difference between kids who went to preschool and those who didn't. It does help them get ready for kinder, though. My son's kinder teacher always talks abt how the kids who went to preschool are much easier to teach, because they come in already knowing that they have to follow the schedule, have to sit in their chairs, etc etc...The ones who are coming to school for the first time have to be taught all that stuff first, which eats into instruction time.
My eldest was a quiet child, ready to please and follow rules, so he was fine in kinder, even though he skipped preschool. My second one went to preschool when he was 4, for 2 1/2 hrs a day. He was a little terror, and one of the least well-behaved kids in the class...mostly running around, not able to sit still, etc etc...but this year, he's in kinder, and he has been a model student. Maybe preschool calmed him down, or maybe he just needed to be a bit more mature...dont know for sure...
So yeah, I think it has its advantages, but 3 yrs is too young, I think. At 3, they need mommy, and sometimes even still at 4...