In fact this is enshrined as an official corporate policy - engineers get 20% of their time to do with pretty much as they please, and are judged in part on how they use that time. I found a speech claiming that over half of Google's applications started as a 20% project. >> (I'm surprised that the figure is so low.) I wonder why you are surprised? Actually it's very high. Imagine Google don't offer 20% for its' empl…
Usually, people use the official personal time to take mini-sabbaticals with other projects, or write tools to make their own lives easier (which may have more general use within the company, or beyond.)