Our daughter is only 16 months old right now, but we have every intention of taking trips when the opportunity presents itself and not based on the school year.
My mother was a teacher, DH's mom was a teacher, and I have two sister in laws who are teachers. DH and I both took vacations with our family during school times (in my case, during weeks when my mom wasn't teaching due to different schedules between my school and the school system she worked for, in DH's case with just his dad) with full approval of our teacher moms.
Yes, education is important. But so is learning at its most spontaneous, when we learn for pleasure and out of our inquisitive natures and a sense of wonder rather than out of rote and by rule. What an interested kid can learn at Animal Kingdom at WDW, while kayaking through a tidal marsh on a
DCL cruise, touring a castle on an
Adventures by Disney trip or just camping out in the middle of nowhere blows out of the water what they could have learned in that same time sitting at a school desk.
Also, honestly? I don't care if my daughters grades take a hit as long as her learning doesn't. I had abysmal grades through middle and high school and yet managed a 3.7 GPA in University and a 3.8 getting my Masters degree. No one has ever asked to see my high school grades since I applied for college, let alone my middle or grade school report cards in the 'real world' and quite frankly, they never will.
Of course, this is different for every child. I am sure there are reasons that some kids simply can't be pulled out of school for their own good. But the decision should be based on the child, and not on the school.