PaaS will tend to be open source and come in flavors
An excellent discussion of PaaS, Ric, and some telling points on how standards and open source code will have a lot to say about which types of PaaS survive and thrive. VMware/Pivotal had good foresight to build a successful open source project around Cloud Foundry. More power to them. Google App Engine and Microsoft Azure are different beasts where the PaaS closely resembles the infrastructure as a service itself, and applications that developers compose there should probably be run there. Red Hat OpenShift will bring additional standards and open source, with expertise in the Linux kernel and Linux Containers. It may develop its own distinctive flavor of PaaS.