I flew AC 3.0 (rc5) at Sparkfun which required me to rethink my vibration dampening strategy. In other words I had to go from no strategy to something very robust. If you want to fly 3.0 in any AP mode you'll need to consider at least some of these methods. Once upgraded, my copter was able to hold a 1 foot loiter box with the crappiest RCTimer props/motors they sell without issue.
Here was my shopping list:
I attached the latex foam to the vibration mount with super glue which worked nicely. Adding the dollar coins with super glue under the floating vibration mount also worked well.
Even with motors vibrating so much that they looked burry, it still held a great loiter.