Americans excel at many things. Vacationing isn't one of them. Year after year, labor surveys reveal that millions of U.S. workers fail to take their allotted time off. A study from the U.S. Travel Association shows that 54 percent of Americans ended 2016 with unused vacation days. Collectively, the nation skipped 662 million days of annual leave during the year, including 206 million days that cannot be rolled over or exchanged for money.