We school year round, taking time when we need/want it. We don't follow a schedule or plan, just keep pushing forward. We usually school 5 days a week, but I will easily drop a school day for a day at the beach, or a visit to the museum. We also take a week or two here and there for vacations, Christmas, etc. We sometimes work weekends if we are in the mood, or there wasn't much work done that week. My boys are at grade level or ahead in all subjects, and none of us ever feel burnt out.
That reminds me, I don't think I shared my homeschool mum interview from the Pioneer Woman here, I talked a little about our year round approach there. http://thepioneerwoman.com/homeschooling/2014/01/homeschool-mom-interviews-irishmum/