Why bother? A few reasons: First, hybrid cloud apps can quickly scale up and scale downas your needs change and without you having to buy and provision your own servers. Companies such as Boeing and Varian use these clouds to perform complex mathematical calculations when they need to have a lot of computing horsepower at their disposal, and then shut everything down when the work is finished.

Second, you can spread your risk across multiple data centers effortlessly, and these data centers can span the globe without you having to invest in your own infrastructure to connect them. This can make it easier to be seen as a global business, at the same time providing for a more reliable network too. Hybrid clouds are also more secure than pure public clouds, since they are protected by your own firewalls and other network security apparatus. For example, Amazon Web Services offers its Direct Connect, GoGrid offers its CloudBridge andMicrosoft Azure has its Virtual Network — all three allow you to have dedicated and secure connections from their cloud servers to your data center.

And the cost can be pretty compelling too. Amazon’s Web Services offers a special “free tier” to any new customer with a wide variety of offerings to help you get started. For most situations, you only pay for time the equipment is online and being used.

The cloud platform players are making it easier to deploy hybrid clouds and are putting more infrastructure services into their product lines, such as network management or the ability to automatically balance application loads across multiple servers. Joyent’s private cloud offering and zScaler’s cloud are two such examples. The platform players are also expanding the kinds of servers, protocols and applications they support, such as Amazon adding Hadoop servers, VMware’s vCloud line and Rackspace getting behind CloudStack.

What makes the most sense for your first hybrid cloud app? Consider those that place peak demands on your existing data center, such as compute-heavy tasks or seasonal spikes. Look for Internet-facing apps such as eCommerce that are already using a great deal of cloud-ready infrastructure, or apps that will be accessed from a variety of geographically-dispersed locations. Apps that depend on particular latency or bandwidth levels aren’t good candidates, because these will be harder to deliver across a hybrid cloud infrastructure.

Finally, set the right expectations. “It all starts with design,” says Bryan Doerr, the CTO of Town and Country, Mo. cloud provider Savvis. “Make sure you understand the performance and security characteristics of the cloud, so that you can achieve the levels you expect.”