I've only been on three cruises and never saw the "chair hog" issue until my last cruise. People put towels on the chairs very early in the morning, and then sometimes never even used them all day.
One day, my friend and I went out and saw that about half of the chairs were empty but had a towel. All day, every day, there was never any open chair. And SO...we hung out for about twenty minutes and saw a line of chairs with towels but no people. So we moved the towels and sunned ourselves for about two hours. No one ever came!
Royal Caribbean Vision - Mexican Riviera 2008
Norwegian Pride of America - Hawaiian Islands 2009
Until the "Kellie in the Morning" Cruise on the Norwegian Star