I don't know how many are fleeing, but a whole lot are very upset about IOS 6 bugs and battery issues on the iPhone 5. My current WAG is that Apple didn't study very well latest spin on the A6. It seems to be burning up the battery at a very high rate in comparison to the iPhone 4s and way, way worse than the chip in the iPhone 4.
These are basic QA issues and another WAG is that such a thing wouldn't have happened under Jobs.