[fredophile]

Where I work we don't get 20% but we do get 1 day a month (so about 5%). We're a lot smaller than Google.

When I first started with the company I used the time to gain experience using the products we make. That gave me more insight into our user's perspectives and paid dividends in future tasks like bug fixing.

Sometimes people use the time for small things that they want to add but aren't important enough to be scheduled. I work with people that are passionate about what we do so it's nice to be able to make improvements in the spots we care about.

Sometimes people will use the time to throw together a proof of concept for a bigger feature. The real feature might take months to get working to the point where it is stable and polished enough for an end user but you can get a lot of management buy in if you have something tangible that can show people what the feature could do.