I must preface this reply by saying even though I myself would not take my children out of school for vacation, I have nothing against a parent that chooses to do this. You know your children best and know what is best for your family.
I always find the "whether or not to take your kid out of school for vacation" threads interesting. The reason is, I am a social worker that works with children who have excessive absences. I am employed by the state, and the county in which I work has a very strict truancy policy, once the child has missed a certain number of days they are referred to us (DHHR or DHS is some states).
Most of my job consists of working with teens that are criminal or status offenders and truancy falls in the category of a juvenile status offense (status offenses are things you can get in trouble for as a child but not as an adult i.e. smoking, truancy, running away). Once the referral is received on a truant child we must make contact with the family to determine the reason for the absences. In my experience, if the child is under 10 and continues to be truant the parents are arrested and must answer to a magistrate judge. If the child is over 10, the child is charged as a status offender and must answer to a circuit court judge. In the past year, 8 kids on my caseload ages 10 and up were removed from the home (temporarily placed in states custody) and placed in facilities that would force them to attend school. Granted, these are extreme situations, most of the kids were 13+ and two of the children had not attended school in 3+ years.
Even though the truancy policy is strict it has greatly increased attendance in the county in the past few years it has been in effect. The policy is generous in allowing for 6 excuses written by a parent (per year) therefore if one wanted to go to WDW for a week they could write a note to cover the 5 missed school days. I have once gotten the WDW excuse which made me pretty jealous of their trip

! But, I still had to explain the rules and monitor the case throughout the end of the school year.
So, the morale of this very long reply is make sure you know your school, state or county attendance policy. Make sure you turn in those excuses, always get one from the doctor if the child is sick. Always keep in contact with your child's school. And, if the social worker or truancy officer shows up at your door, be nice, explain the absences, and if you're willing to work with them they will normally bend over backwards to help...at least I know I would.