Private cloud can be a very confusing term. The whole point and promise of the cloud is that its managed by someone else. For a few very large organizations private clouds make sense, but for most businesses, especially those in the SME space, it makes much more sense to leverage public clouds. With the right approach, public clouds are MORE secure and MORE safe than private clouds.
Amazon S3 is a good example, they can sustain 2 simultaneous data center losses and still return your data. Are you going to provide this kind of redundancy to your business when you set up your private cloud? Have you calculated all your costs of running a private cloud?
Again, it can make sense to have a private cloud in some circumstances, but for the rest a solid solution like the Nasuni Filer mentioned in this article may be the way to go. For more information visit http://www.nasuni.com or read our thoughts on private vs. public clouds at http://goo.gl/L9NmJ.