From following the technical evidence on both sides in the Pinder v Fox court case my personal advice on QRs is here:
1) Disk braking forces can create lateral forces at the screw nut/drop out interface SUFFICIENT TO UNWIND THE SCREW NUT.
2) Worn cams can reduce the resultant tension force in the skewer by up to 50% from that which an unworn cam would generate given THE SAME AMOUNT OF FORCE APPLIED TO CLOSE THE QR LEVER.
3) Alloy screw nuts on steel skewers can wear such that THE NUT IS SUSCEPTIBLE TO UNWINDING THROUGH VIBRATION ONCE TENSION IS LOST IN THE SKEWER
4) Plastic locking inserts in screwing nuts can significantly REDUCE THE EFFECT OF VIBRATION ON THE SCREWING NUT
5) Plastic locking inserts can ALSO WEAR OUT OVER TIME
6) Loose screwing nuts CAN UNWIND VERY QUICKLY THROUGH VIBRATION
http://spoomplim.blogspot.com/
The most important component in this, I believe, after a good condition cam plate, is the plastic locking insert in the nut end. I dont have any info on which QRs do and do not have the insert, but you should be able to tell simply by feel when you wind/unwind by hand. I believe shimano ones do have the insert.