A useful side benefit of Cloud Computing is “security through obscurity.”  Not in the flawed, shared-secret sense of the phrase, but rather because of the cloud’s transient nature.

Infrastructure run in the cloud does not need to be turned on 24/7.  In fact, you are motivated to turn off resources in the cloud since you are charged by the hour.  In the cloud, you should not have a number unnecessary zombie servers running 24/7 that are vulnerable to attack.  Servers with missing Windows patches never need to be turned on.  And while that does not make the servers you do run any more or less secure, it will cut down on the number of unnecessary machines that carry a real risk to you and your customers.