I have worked as a PhD student and (academic) postdoc in several european countries, and have formally been allowed between 25 and 38 days of holiday per year, as well as public holidays (which can add an extra 10 or so days). That said, not all the institutions where I worked were rigorous about registering everyone's vacation days. Also I don't see professors using their full vacation allowance - typically they take 2 weeks off in the summer and a week off over xmas. Some years I don't use all the available vacation days, but since I live away from my home country, it's important to me to have the flexibility to go back home to see family/friends. Some of our staff from more far-flung places (asia etc) will use many vacation days in one block (3-6 weeks) to go back home, since flights are expensive and they can only afford to visit once or twice a year. One thing that seriously put me off working in the US was the lack of vacation days. I don't know if we are more productive over here, in terms of volume of work done, but I know personally that I produce better quality work when I am properly rested.