I am not an advocate of public clouds nor i am looking down upon the idea of privately managed clouds. Both have some cool USP that makes them attractive for particular use cases
Here is what Gartner had to say as to why 95% of the private cloud deployments fail.
When people consider private clouds, often they underestimate the cost of maintaining, upgrading and scaling the privately provisioned clouds. Most of the times, this cost is much more than opting for the public clouds.
Some might argue that Openstack could be the answer to all the problems but “Vanilla Openstack” is just a Myth. One would require setting up of multiple components or frameworks (read more about that here). Also with a major release every 6 months Openstack is evolving very rapidly in multiple directions. Also a point to note here is that most of these components have varying degree of maturity.
Agreed that Openstack promotes Vendor neutrality. But then we have the likes of Netflix(and many more) who are perfectly happy with Amazon.
At this point of time, there is no clear answer to this question. May be 95% of the people had wrong(or too much) expectations. So i would like to conclude by saying that private cloud are definitely great provided the organization has sufficient bandwidth in terms of talent pool coupled with the $$$ and the architectural vision and roadmap that can ensure the private cloud is a success story.