Nati Shalom – Private/Public Cloud:

"It is clear that to make IT operations more effective, it doesn't make sense to run all the applications that are currently hosted in a company's data center in the private cloud.

[…] Disaster recovery sites require us to double our resources, let alone the cost associated with maintaining two separate data centers. These are classic scenarios in which running applications on a public cloud could lead to huge cost savings."

(Via High Scalability.)