I am strongly opposed to memorized pre-flight checklists, because it's
too easy to be distracted or forgetful and miss something important.
I require my students to refer to a printed pre-flight checklist and
complete each step in order, and I use one in my own glider. I
believe that too many accidents have been caused by poor preflight
checklist completion--there are too many accident reports citing poor
checklist discipline as a factor. Preflight is a time when the pilot
can take his/her time to do it right, and refuse to allow any
distractions and not be rushed. That printed checklist is a powerful
tool, and should be used as such, every time!

Inflight, it's a different story. There is too much going on--
clearing, flying, planning--to be burying one's head in the cockpit
and reading a checklist. The pre-maneuver and before landing
checklists must be SIMPLE and memorized. Adding things like "look"
and "land" just garbages them up. Checklists are supposed to be
specific actions to configure the glider or prepare for an event.
Switches, controls, straps, checking the wind and airbrakes all fall
in this category. Doing what we are supposed to be doing does not.