Personally, I read in the cockpit all the time. We have a cockpit door, which is always closed, so it's never an issue anyway. On the other hand, I probably wouldn't read if I had anyone on the j/s, for example, or was in anybody's direct view.
It's not so much because I'm frightened to "make the passengers nervous" or being viewed as unprofessional or anything like that.
Let's say you have an incident or accident of some sort. In this f'd up world of frivolous lawsuits, I wouldn't put it past some idiot passenger to make some stupid accusation that he saw the pilots reading and his team of lawyers are coming after you for negligence or some s**t.
I heard a story about some airline passenger (who happened to be a private pilot) that upon landing, approached the crew and accused them of exceeding 250 under 10,000. It turns out he had a handheld GPS with him. I guess that private pilot doesn't understand the difference between groundspeed and indicated airspeed.
Call me paranoid, but there always seems to be somebody looking for any reason to complain about a pilot.