1. A tangible non-transitory computer-readable memory having instructions stored thereon that, when executed, cause a processor to perform operations comprising: determining that a first playback device is active in a first bonded zone, wherein the first bonded zone comprises a second playback device of a first zone group, wherein when the first playback device is active in the first bonded zone the first and second playback devices of the first bonded zone are configured to synchronously play back different portions of first audio content; after the determining, detecting that the first playback device has become inactive in the first bonded zone; and in response to the detecting, sharing the first playback device with a second zone group comprising a third playback device but not comprising the second playback device, wherein the sharing includes enabling the first playback device to be active in a second bonded zone, wherein the second bonded zone comprises the first playback device and the third playback device, and wherein the first and third playback devices are configured to synchronously play back different portions of second audio content when the first playback device is active in the second bonded zone and inactive in the first bonded zone, the first bonded zone not comprising the third playback device.