I agree, and I'm also careful not to leave boarding pass/itinerary/receipt in an airport lounge unattended or visible in my hotel room or office. It's an easy precaution to take.

OTOH, I remember staying at the same hotel as some top executives during the NW/DL merger and I was shocked to find that employees were very careless about information left behind in the business center: financial spreadsheets and merger plans left in the printer (maybe these were just drafts, but such documents shouldn't be public), email accounts, and flight PNRs. It would have been so easy to change the CEO's seat assignment (or worse) but I didn't. Maybe they believed that their group had taken over the entire hotel, but even so, during a merger, some employees are likely to be disgruntled.