I think the higher up in the org you are, or the more you serve as a bottleneck for productivity (e.g. because of unique skills), then the harder it is to take a truly 100% off vacation. The terminal example is a CEO — I'm sure most CEOs would cut a vacation short if a real crisis came up. That said, it has to be an actual crisis. If coworkers are bugging you about routine stuff on vacation, that's a bad work environment.