Today, for no particular reason, I made a list of all that managers that I've had at my day job. In the past eleven years, I've had nine managers. Five of those managers have left the the division, or company for somewhat murky reasons.

One for sexual harrasment.
One for never saying no to any request, but never delivering anything. That one got away with it for years before someone realized his team was a black hole of work.
One for promsing to fix an important problem, but never fixing it for years. That one was the guy who promoted me to manager.
Two left for having a bad relationship with their boss and being on the loosing end of the argument.