Do you have a vacation planned this Memorial Day weekend? If you do, you might be working extra hard around the office to make sure everything is taken care of. Vacations have a wonderful effect on the work day -- they make you work harder and more effectively.  It's surprising Americans typically only are allowed two vacations a year. If time off were more common, employers might find their employees clearing off their desks, ticking off of to-do items, and enjoying everyday tasks with a little more than average enthusiasm. Time off encourages productivity. In that spirit, a little-known "holiday" was created by productivity expert Laura Stack. Wednesday June 2 is National