I am happy to report that I have achieved a major victory in the battle against the loathed Jello Effect - the asymmetric video motion caused by the high-frequency mechanical vibration. I run a hex setup with a 2-axis gimbal and the GoPro HD Hero 3 Camera.
Step 1: Replacing stock plastic props with carbon fiber was the first and most significant factor reducing vibration from 1.8 to 0.3 even without balancing, but it did not solve the problem completely.
Step 2: Placing silicone rubber between the camera and the frame and ensuring there is no contact anywhere has done the did. Before, I have tried pretty much everything including foam, rubber, various mechanical setups but nothing worked as well as silicone.
See the video for more details: