Il me semble avoir déjà parlé de cette (aujourd’hui) légende, mais une réponse sur Quora vient apporter de l’eau bénite à mon moulin. Donc je la publie. C’est écrit par Joel Johnson, ancien employé de Google au sein de l’équipe Adwords :

Google: How does Google’s Google Innovation Time Off (20% time) policy work in practice?

While I was there (2010), the group I was in (AdWords Campaign Management) discouraged any 20% project that wasn’t a feature for the group’s product. Actually, they discouraged it period. But they never said this explicitly, they would always do it in a roundabout way.

If you ever decided to take on a 20% project, they wouldn’t say no or block you explicitly, you would just start feeling the grumbling and the side effects of going against their wishes everywhere you’d go.