"Virtually no Google engineers use their personal time to develop new projects."<p>I've tried, without success so far, though I've got a bunch of things in the half-done state that could turn into something useful eventually.  It is <i>very</i> hard, kinda like starting up a company while keeping your day job.<p>I've found I had the most success by just trying to get my 80% project out of the way as fast as possible, doing as much as needed to keep my teammates happy, and then banking the remaining time to work on 20% projects.  It's best used in chunks of a week or so, so that you can actually finish a lot and have something concrete that can sit and wait for your next big chunk of time.