At EMCWorld I learned about the worlds first open-source cloud framework – http://cloudfoundry.com/. Developed by ex Google employees, this is a ground up Platform as a Service (Paas) environment that allows the enterprise, private, and public clouds to benefit from the same features, functions, and APIs.
Now, you can develop LOB apps on the platform and keep it secure behind your corporate firewall. Then, when the need is great enough, you can migrate it to a public cloud, or enable your private cloud available on the internet.
No longer is PaaS an all-or-nothing situation. You can integrate your internal thick apps with your internal cloud apps.