Vacation is your safe haven from work's demands. For the Engineer Adventurer it's one of the few tools that returns complete control of life for a period of time. Weekends and holidays barely allow the time to escape the city, much less the cramped mentality of work.
Across the spectrum of engineering jobs there is a large variation in the amount of vacation given each year. My first out-of-school job started with a measly two weeks of vacation per year and topped out at three weeks after years of service. At the other end of the spectrum, I've worked for a company that started their newest hires with four weeks and after many years of service award up to eight weeks.
Of all the benefits an employer provides, vacation must qualify as the most grudgingly awarded. I've heard bosses and HR personnel extol the virtues of 401k matching, the gym, and health care. But I seldom hear them encourage employees to take vacation.
Even when the boss isn't pleading for you to stay, the pace of work discourages taking time off. The barrage of meetings, emails, and instant messages make it feel impossible to escape the office without falling hopelessly behind. 50 or 80 hour work weeks make it sound impossible. Vacation time gets pushed behind the piles of late projects, guilt, and panic.
Ironically, I haven't personally found a large difference in attitudes between companies with skimpy vacation and those with generous vacation. Under both circumstances I commonly heard of colleagues losing vacation hours because they weren't using them. Some of the colleagues seem bemused or proud of the fact. Others seem resentful that their life takes second place to the sometimes silly demands of work.
In either case, the attitudes of one company and another with twice the allowed vacation are similar. I suspect that the real problem isn't the amount of vacation. Instead, poor planning, low productivity, or unrealistic expectations probably create the tension surrounding time off.
Use your vacation, don't let work run your life. Your boss is a supervisor, not a slave driver. You can replace your job -- probably with a better one that lets you actually take vacation promised to you. Your colleagues will survive without you, just as you survive when they are out. Don't let work steal your time while it so often squanders it's own time on activities that don't contribute to the bottom line.