are these cameras easy to operate? i hear that people have had problems with there sd cards, is this true? or do you just stick the sd card in and your ready to go? i noticed on the back of the camera there is a sensitivity knob where does everybody put theres half-way, a quarter, etc.? and does the viewing screen stay off, when your not around? how long do the batteries last in lets say 10 to 20 degree weather?