I hate it myself. My boss made everyone reposition their computers so that he could see the screens as he walks down the hallway. He seems to believe that if you do anything besides work while you're sitting at your desk -- to include during lunch -- you're stealing from him. (He doesn't believe in breaks. This from the man who's out of the office about 70% of the time doing God knows what, particularly on Fridays.
Of course, he once accused me of playing a game because he saw me defragmenting my hard drives.
Reallly? Because much of the work my company pays me for is confidential--student information, budget including salaries, HR work such as hiring, terminations, and disciplinary actions. So, yeah, it wouldn't just bother me if someone was reading over my shoulder without my permission but it would bother my boss and HR, as well.
It's rude and unprofessional to sneak up behind someone and read over their shoulder.