ORIGINAL: trab1925
For some reason I am finding it hard to believe that checking servo arm connections should be on everyone's pre-flight checklist. I could see this being something that could be easily overlooked no matter how much experience you have. I don't know about you guys but I don't inspect each servo before every flight other than going by sound/malfunction. It is interesting though that the screw managed to work itself out from the time you did the control surface check to getting it in the air while still managing to keep itself in the servo arm after landing. Is it possible you just didn't notice that it wasn't working correctly when you did your surface control check?
It may not be every flight, but I visually check my servo control arm screws each time I assemble a plane. It is very rare, but I have had a couple back out and my preflight caught them. I have several planes that have aileron servos that are recessed(hidden) in the wing. On these I grasp the servo control arm and see if there is any wiggle or looseness.