I agree that the fundamental concern was how to show something conceptual in a visual context where books and printed papers would be considered ancient artifac

I agree that the fundamental concern was how to show something conceptual in a visual context where books and printed papers would be considered ancient artifacts. After watching a couple of scenes with Picard having several PADDs on his desk it occurred to me that I was presupposing that those devices were personal property. But in that future personal property is largely for sentimental items, not utilitarian ones. Also, the PADDs are primarily computer iterfaces. If you posit that PADDs are as ubiquitous and disposable in the future as Post-It notes and thumb drives are today, the metaphor makes sense. (Indeed, considering the inevitable price drop of consumer electronics, we aren't that far away from iPadish tablet computers reaching that point.) So Riker picks up a "blank" PADD, his DNA and thumbprint or whatever identifies the device to the network as a Riker interface for the time being. After he's composed his mix tape or status report on the device, it's also resident on the network. And when he hands that PADD to Picard, the recognition of the transfer to Picard serves to automatically track the work flow and acknowledge Picard's acceptance of the report.