We school year round, but take days off liberally when we need to. During the summer we sometimes miss a week here and there for VBS (we sometimes still try to get some school done in the afternoons) or visits to grandparents.
We try to start reasonably early on summer days and get as much done as we can before the neighbor kids are out. We try to be flexible in how much we get done and when we do it to give them as much playtime as possible.