The air regulations require checklists, and pilots can fail flight tests for improper checklist use, even if they actually completed all the required items, but it doesn't mean every pilot uses one every time. Some operators inadvertently encourage this through providing overly long, poorly formatted and difficult to use checklists.
In my career I have watched macho captains deliberately skip checklist items, or even entire checklists. I have been bullied for using the checklist, and told not to come back tomorrow unless I had the checklist memorized. I know someone who failed a PPC check on an accusation of improper checklist use. (It turned out the examiner was using the wrong checklist, so that occurrence magically disappeared from the candidate's record).
Despite pilot machismo, or passenger apprehension that following a checklist means you don't know what you're doing, checklists are a cheap, simple way to improve safety in a complex environment. A reader sent me this fascinating article on checklist use in the medical profession. The idea was initially met with skepticism, and derided as time wasting, but the lifesaving results were dramatic enough to win converts.
It made me cry, and gave me a new dedication to my own checklists.