Earlier quoted context omitted.
I know many people at Google Boston (Cambridge). They are all bored out of their skulls. One guy says how he works 30 hours in a busy week and uses his 20% time to hit the gym. But in another's words: "how can I leave when they pay me so much?"
I work at Google Cambridge, and I'm easily working 50+ hours a week. I work in Technical Infrastructure (on our storage systems in our data centers) and one of my 20% projects was to design and architect the underpinnings of what an Android Product Manager has claimed to be one the most important features of Android N (file based encryption), the open source incarnation of which (ext4 encryption) has turned into a ge…
When you say it "You'll be working 40 hrs a week and to be successful you'll need to spend an additional 25% of your time coming up with other stuff that helps us." it doesn't sound quite so magical :-)
That said, when I worked there I quickly realized that with no trouble at all I could spend all my waking hours in the office playing with the neat things that are made available to employees. It doesn't feel like overtime when its something you would do in your free time anyway.
The sticky bit is that you don't get profit participation in the financial upside of those extra projects.