I hate to point these out because I don't agree with them, but there are a couple of interesting columns on AvWeb about exactly this topic:
Throw away that stupid checklist!
http://www.avweb.com/articles/pelperch/pelp0001.html
Checklists redux
http://www.avweb.com/articles/pelperch/pelp0002.html
The interesting common link between John Deakin who wrote the above columns, Centaurus and all the pilots in Centaurus's examples is that they are all full-time pros who are immersed in aviation. If they don't fly every day, then it's at least every week or a few times a month. When was the last time the John Deakin or the 'gnarled old Super Connie engineer' had a month when they didn't even think about airplanes? Probably before puberty! That makes a huge difference which I don't think they appreciate.
Something that may be second nature to them certainly isn't to me. With up to a month between flights, it would only be a matter of time before I started forgetting to check some things - maybe that the doors are shut properly. And once you've started forgetting things it seems normal not to check them because that's what you did last time. Nobody's going to point it out until the next check flight. Sure, taking off with a door unlocked isn't by itself a killer, but it could easily be one of those links in a chain that you often see in accident reports.