"if 20% time has been abandoned at Google, are other companies, which reportedly include Apple, LinkedIn, 3M and a host of others, wise to continue trying to copy it?"
That's incorrect, AFAIK 3M were the first company to pioneer this approach (with 15% of time spent on self-directed projects).
For example see: http://www.fastcodesign.com/1663137/how-3m-gave-everyone-day...
Talking to a friend at 3M (who has been there 20+ years, an engineer with dozens of patents) I am told that while 15% officially still exists, for a long time it's effectively meant working 115% of hours.
Nonetheless the tradition allowing self-directed research continues at 3M - and this might mean using lab resources, or creating prototypes without getting approval.
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