Many IT “infrastructure as a Service” providers offer hybrid cloud services allowing you to purchase compute services as needed based on your peak. Cloud computing is still a couple years away mainly because only a few players are offering the “brokering” service that is required to make it easy to purchase computer (i.e. cpu, memory or storage) resources on demand.
The most significant benefit of Cloud computing is elasticity, which is the ability to automatically scale out based on demand and users’ quality of service requests. Having a VPN set-up with dynamic provisioning allows you to do this. Alternatively, set up a broker between the private network and the cloud provider and to manage traffic/demand based on pre-defined security policies.