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I would put #2 as #1 and #5 and #2. Billing is a huge technical issue that can consume a great deal of resources to respond to. Performance is a BIG issue as far as server environment are concerned. Desktops can run slow without end users really noticing a difference from their current desktops. Servers on the other hand need speed and cloud environments don't fair well here unless you have huge budgets. Bandwidth not such a huge issue unless the cloud provider makes it one.
#1 issue of security I see more a matter of managing process implementation. It just takes some well thought out processes to deal with all of that. This should be around #3 I would say. Not to suggest security should take a back seat, but in this breakdown of what challenges cloud has.. this is where that challenge belongs in my opinion if we are listing based on the degree of difficulty in addressing the challenges.
1 year, 6 months ago on Top Five Challenges Of Cloud Computing