Spent two years flying Barons and Aerostars in Part 135 frieght. Did a run up at the beginning of the night and if I changed airplanes during the night. Otherwise, didn't bother again. Now, this does not mean I didn't use the checklist. Checklist is used every time! I do basically the same thing with my Pacer.
If I add gas, yes I check for water. Again, checklist is used every time!
Jim
(Yep, I'm expecting flames on this one!)