Google is famous for their 20% policy. Where their creative people are allowed 20% of their normal work-time to work on untracked projects. This is where some famous products have come from. It's a way for Google to further capture the wisdom of crowds in coming up with interesting projects to capture more market.
A 20% policy, one day a week, is a very admirable thing and has been copied many places. However, it is not a stable policy over the long-haul without a lot of maintenance work from On High. The normal give and take of business means increasing output from said creative professionals is a sound business move; a 20% policy deliberately introduces inefficiencies into that, and runs counter to how things work.
I looks like Google has given in on the maintenance work. They've introduced Stack Ranking into their management structure, which is exactly the kind of disincentive needed to turn 20% time into 20%-overtime (or 120% time as they seem to be calling it). How Google is using Stack Ranking is to identify the bottom 20% of their creative professionals and get them mentoring or other help to get them to do better. It's employment enrichment, and helps the company as a whole maintain a productive workforce.
However, to those creative professionals it sounds like...
We've noticed you suck. How can we help you suck less?
Which is a really, really great way to get people to stop using their 20% time and focus 100% on the job they're paid for, and seem to be at risk of losing. If they've got any 20% projects going... they'll be sidelined or pushed into after-work territory.
This effect extends to the entire workforce, as the specter of the Grim Disapprover coming for the slowest 20% is a good incentive to not be in that 20%. So perhaps I should give more time to my tracked projects? Yeah...
And now the 20% policy is a 120% time policy.
This is a more metastable state than the old 20% policy was. Google gets 100% out all but their most self-assured employees, and the really motivated are working away on projects that could be big in the future. The only cost is allowing 'personal use' of the Google Infrastructure. Even better, those really-motivated employees are doing this work beyond what they'd normally give to just daily work!
20% time, as originally implemented, is a great way for a company to innovate massively to gain entry into many markets. The Google of 2002 needed that. The Google of 2013 doesn't so much. Backsliding into a more stable state makes sense.