All,
There's been a bit of delay in posting this because I lost the photo!
Here's a picture of a standard aluminium motor mount after just ONE FLIGHT!

This mount was originally on my Whizza. I power tested the aircraft on the bench and then Chris Bott test flew it for me a couple of days later.
Motor test took about 4 - 5 minutes and the test flight was no more than about 3 minutes.
Also, the NTM Series motors are factory balanced (and they are) plus my props are all balanced, so vibration is minimal.
Complete structural failure of all four arms!
This mount came as part of the accessory pack for an NTM PropDrive 36-35 motor from Hobbyking. It had never been used on anything else.
I've since noticed (and brought) carbon fibre versions of the same mounting from Hobbyking.
Do Hobbyking know that they've got a quality control issue with these aluminium mounts?