On the one hand, public cloud is rapidly replacing external services spend at many companies. After all, why wait for IT to provide a service when you can just pull out your credit card and buy a ready-made one from Amazon or Rackspace? So external services spend is being cannibalised.

On the other hand, public cloud adoption is encouraging organisations to get their non-public workloads off-premise and into a service provider. A November 2012 Gartner report notes Infrastructure as a Service (IaaS) adoption — the most basic and fundamental form of cloud computing service — has expanded beyond development and testing and is now used for production at a significantly large number of organisations.