Wendy Kallergis remembers her early days in the hospitality business with some exhaustion.“My job is a Monday-through-Friday job,” said Kallergis, president and CEO of the Greater Miami & The Beaches Hotel Association. “But when I was working at hotels — and in catering, particularly — we would boast about how many days straight we worked.” That kind of work ethic (some would say over-zealousness) is getting a critical look these days as American workers leave more vacation time unused.According to Project: Time Off, a U.S. Travel Association initiative, American workers lost 169 million vacation days in 2013.