Last cruise we had hundreds of dollars worth of electronics sitting out every day on the desk. This could include, at any given moment, my laptop, one or two ipods, one or two digital cameras, camcorder, etc. We did this the first few days. One day, I returned to the room while our steward was cleaning to grab something. The door was propped open with a wooden shim and no one was in the room. I can't remember where I saw the room steward; he was close by but anyone could have popped in, picked something off the desk and popped out without his knowledge. I don't believe he even saw me when I came in, if I remember right. From then on our items went into a drawer under something or into the safe.
I also noticed this as we walked by other rooms during the cruise. While the steward is off, nearby but not in the room, the room is left wide open.