Our servers are due for refresh, so I'm evaluating moving our web servers to a cloud provider - but I've done substantial research on costs, the results showed its only marginally cheaper to relocate our existing systems.
If we kept our Colo and purchased new servers, the cost would be about 5-10% (payment spread across 3 years) more expensive, but it would give 2-3x the capacity of what we currently have..
So in the short term its cheaper to move to a cloud, but we're currently experiencing exponential growth, so the medium term it could work out much more expensive. Then the high profile outages of EC2 and Azure, highlights the support issues and lack of accountability.. I suspect this is a major concern for all IT Managers. After all, we're fundamentally reliquishing control, there is little we can do when outages occur, but we're still ultimate responsible for keeping things running..