Unless you have had your head buried in the sand lately, you have by now heard of the term cloud computing. Cloud computing can be defined as service-based computing, where a company buys software or storage as a service (SaaS) from an internal or external provider.
A good example of cloud computing in action is e-mail from either Yahoo or Google. Instead of running your own mail servers, you simply allow your employees to use the services provided by those companies to eliminate the capital costs of doing it yourself. You may not have complete control, or get everything your heart desires in a mail solution, but the price sure is right. It will be interesting to see how long these companies can go without charging for these services.
http://blogs.computerworld.com/15252/what_is_the_killer_app_for_cloud_computing
The desire for companies to reduce costs and focus IT on core business applications which can increase profits and shareholder value brings us to the killer apps for the cloud.