For people who have issues with this, I'd suggest asking your manager or whoever is in charge whether X days of vacation per year would be acceptable. And then track your own vacation days and treat them like you would at any other company.
Manager: "Take as much time as you want, but know that your absence would be highly disruptive to the company."
yes, but you also don't get paid out vacation time when you leave, and there's always this social pressure to not take long trips (3 weeks, anyone?)