For starters, the infrastructure as a service market will peak at $5.9 billion in global revenue in 2014 and then commoditization, price pressure and falling margins kick in. In other words, early wins by Amazon Web Services and Rackspace won't add up in the long run.
Software as a service will be adopted by companies of all sizes. In 2011, SaaS will be a $21.2 billion market and grow to $92.8 billion in 2016. AT that point SaaS comes closer to saturation.
BusinessProcess as a service will be notable, but face modest revenue.
Virtualization will recede to the background as new technologies take over.
Here's a look at the big cloud picture through 2020: