Why engage with solution, when the problem has not been defined accurately. Some of the agencies have also concluded that the cost savings, cost avoidance for IT portfolio cannot be established. This is despite the fact that agencies had earlier engaged Gartner wasting millions of dollars to conduct IT Optimization studies.
Erstwhile ITILOB Plan in the link below
When agencies can successfully establish demonstrable clear cost savings and cost avoidance argument, cloud computing as a solution achieving "economy of scale" driven by design considerations might be the inevitable choice.
Mandate must be for the cost savings in IT Infrastructure, Gartner study provides some of the options.
Also, it must not be forgotten that cyber-security is a real growing concern. Google itself has been victim to nefarious attacks. This undermines security related to still unproven and yet promising cloud computing.