John Willis' blog post and Reuven Cohen comments bring up the ongoing debate on cloud ontology. I posted some thoughts on who will win in the different cloud segments around the launch of Microsoft Azure and the new breed of cloud solutions that combine different elements of the stack to solve specific business problems. Skytap is a great example of a solution which doesn't fit neatly into the existing IaaS, PaaS and SaaS taxonomy. It would be convenient to label Skytap Virtual Lab a Infrastructure-as-a-Service offering, but this doesn't capture the rich virtual lab automation application and vertical specific features, such as training workflow for student/instructors. Other cloud management and automation solutions (e.g. Elastra, Rightscale, and potentially CloudSwitch?) also don't fit well into this taxonomy.
The USCB framework is graphically appealing. By adding a cloud solutions vertical bar to the side, it would capture some of the emerging cloud-based solutions that don't fit into the IaaS/PaaS/SaaS model. Over time, I expect to see this category grow and be further classified as new management, automation, interoperability and vertical solutions become available.