When the internet moved beyond the hotmail phenomenon and become a serious contender in enterprise computing; there was the usual media hype about end of IT departments and the imminent move to internet based services. After almost two decades of enterprise grade internet applications, IT departments continue to run certain sets of applications while some applications have moved to the internet.
The value of in-house IT to maintain and run vital business processes was apparent with core applications being maintained in-house. These core applications moved from a client-server to an internet delivery model, but the "network computer" (although a great concept) never really took off. At the same time, internet based functionality provided a completely new level of access to applications, and created entirely new models of business and gave rise to yet unseen businesses (Ex: Webex)
Ultimately the internet was embraced by the enterprise where an appropriate blend of "intranet" and "internet" functions continue to co-exist.
In the cloud arena, similar hype is currently being played out. The end of enterprise IT is trumpeted by popular channels, with an "Everything-as-a-Service" model being proposed as the end-game. These propositions are similar to what the internet went through, and if history holds true, we will eventually end up with a hybrid mix of private and public cloud models of delivery.
The public cloud clearly has value as long as it not used as simply a cost-cutting mechanism. The private cloud would host the enterprise jewels, which would be too precious to host in a public space.