Gartner analyst Tom Bittman is predicting "that the future of corporate IT is in private clouds, essentially flexible computing networks modeled after public providers such as Google and Amazon, yet built and managed internally for each business's users."
While it's true that most enterprises can't replicate the economies of scale that Google and Microsoft have, most companies do have spare computing capacity that can be used as part of an internal cloud.
I've written many times about the need for a virtualized layer--one that separates the platforms and the applications. Gartner agrees and calls this concept a "meta operating system."
Specifically, the meta operating system is "a virtualization layer between applications and distributed computing resources ... that utilizes distributed computing resources to perform scheduling, loading, initiating, supervising applications and error handling."
Bittman also stated that "within five years, a huge percentage of small businesses will get most of their computing resources from external cloud providers," which I would agree with--especially considering that anything that runs on the Internet (e.g., hosted e-mail) in what were formerly known as application service providers are now considered cloud providers.
Clouds will clearly be important and will be clearly be split between internal and external sources. However, the market needs to catch up a bit more both in terms of understanding the use cases and the economic models.