I really like the way The Hoff puts things sometimes:
We’re told we shouldn’t have to worry about the underlying infrastructure with Cloud, that it’s abstracted and someone else’s problem to manage…until it’s not.I think that sums up in one line the problem with Cloud Computing. You are essentially making your job easier by dumping the responsibility for Security (and Availability) onto someone else's plate. Which is fine until they post a note saying "Sorry" and you are left with no service.
Or worse - data that has gone off somewhere that you don't want it going!