To have a cloud as a business model, two things must happen by definition:
1. A user will always have available all resources s/he needs
2. A user will pay only for what it uses
The corollary of the above is that Data Center, outsourced or not, is transforming - for its owners - from a cost center, into a profit center, once it becomes a cloud.
This is major shift that started with Amazon Web Services sending an INVOICE. This natural consequence of having resources available outside the organization - like electricity, virtual nodes, storage and so on - is that the IT Director receives an invoice, and s/ he does not know who should pay for it - triggered a need to keep track of all costs and invoice the responsible parties inside or outside the organization.
In my opinion, the total cost of ownership (TCO) does not tell much about Data Center. The Return on Investment (ROI) tells me not only how much the Data Center costs, but how much money the Data Center - once transformed into a cloud - make. It is the ROI, not the TCO, that gives power to the CIO and justifies its existence and its IT future growth.
No billing, no cloud. But with a cloud - we need the right tool. I learned at Cloud Connect 2012 about Cloud Cruiser.
Cloud Cruiser billing interpretation is deeply rooted in mainframe computing. They must first solve this chicken and the egg challenge, in my humble opinion.