The other half of the problem is of course how to handle these human-received messages ethically and reasonably intuitively. Fortunately, it's easier once we abstract the concrete parts away.
The human-experienced message is much more complicated then the mechanics of manipulating concrete parts. As a result, it is worth its own chapters, such as the chapter on message integrity. But I can give at least one example of a purely "human experience" issue.
There's something called look-and-feel in computer user interfaces, or more generally just the idea of style. When Apple sued Microsoft because Microsoft Windows was too similar to the Macintosh OS, it was strictly a matter of human perception of the software. One of the reasons this case was so controversial is that it was one of the first cases dealing solely with human perceptions, where the flaws of the expression doctrine were painfully obvious. Apple was not accusing Microsoft of ripping off any of the concrete parts it owned: Microsoft did not steal code, they did not steal any significant amounts of text (a few menu commands like "Edit" or "Paste" can hardly be worth a lawsuit), and they did not steal graphics. The graphics were certainly inspired by the Apple graphics, but no more so then any action movie car explosion is inspired by another; similarity is enforced by the similar functions and you can't reasonably claim all graphics that bear any sort of resemblence to your own work. Yet Apple contended that the net result was that the human being using experience of using Windows was too much like the experience of using Macintosh to be legal, that there must be some form of infringement taking place.
It does make some sense that there might be some infringement here, even without any concrete parts being stolen, but it is much more difficult to quantify damages or draw boundaries delimiting who owns what. Another ethical complication is that there is frequently societal benefit to such style copying. We no longer even think about many things that are now very standard styles, such as the beginning of books (cover page, detailed info page, dedication, one of a handful of table-of-content styles, all of which are highly standardized across all companies), the looks of late-generation models of any particular device (there tends to be a lot of convergence into one "final" look for the device; consider the near-uniformity of television designs as the design is dominated by a display area of a certain size, and little else, compared to the era when a television was a small part of a larger cabinet), and other such things. There is great benefit in standardizing on interfaces for all sorts of things, not just software, to reduce the time needed to learn how to use the multitude of objects available to us now.