Google 20% time is a way for engineers to provide justification for resource which they may otherwise be unable to get from their managers, and would have to keep secret (as some managers will object to you doing it in your spare time, too). It's a way to mitigate the productivity drain from managerial micromanagement. Whether or not it works for any given project is subject to many other variables.
Completely disagree. While I was at Google I was encouraged to find another project that I was interested in contributing to in my 20% time. I ended up working on some internal tools, but there's plenty of options.
None of the Google engineers I've met have had 20% projects. They said 20% projects were uncommon in product groups (that have shipping deadlines), but more common in the web teams.
As I commented above, I was encouraged to find a 20% project while there, and I worked on the Android team. Only a few people on my team had 20% projects, but none of them actually wanted a 20% project as far as I can tell. Anyone that did, had one.
