My recently received YN-560 went through a drop test. Rest assured I did not do it intentionally (heaven knows I haven't made a dime out of this blog! :)) ).
My flash dropped from a height of 3 feet to a solid stone floor. It was actually more than just dropped. I was cleaning my bag and shaking off sand (our toddler dumped sand into my camera bag... argh). I thought my zipper was completely closed but it wasn't -- and as I shook the bag downward, the flash fell with a loud bang against the floor. I believe the flash head hit first.
After the drop, the flash was still functioning (including the strange digital optical slave mode)... except for the zoom. When I turn on the flash I can hear a short, loud hum (presumably the zoom motor). When I adjust the zoom, the lights change but the zoom doesn't work anymore. So my unit is stuck at 70mm. :( At least the built-in diffuser still works...
UPDATE: YN-560 fixed!