From the Washington Post:
... research from USTA's Project:Time Off initiative, conducted by the economic analysis firm Oxford Economics, looked at SEC filings for 114 public companies. It found that the average vacation liability per employee is $1,898, and that U.S. companies carried $65.6 billion in accrued paid time-off costs forward on their books last year.
To deal with that liability, companies have several options, says Adam Sacks, president of tourism economics for Oxford Economics. They can actively encourage people to actually use their vacation time. They can make their plan a "use it or lose it" program, where days won't carry over from one year to the next (something roughly a quarter of U.S. companies do now). Or they can adopt an unlimited vacation policy.
"The policy itself encourages employees to take time," Sacks said, "because effectively, they can't get the time back if they don't use it."