Joyent is an infrastructure provider.

Your comments are very similar to some other views. See

http://kevinljackson.blogspot.com/2008/07/my-views-on-classification-of-...

When asked this question, I first describe three layers:

Layer 1 - Hardware virtualization - This is the "bare metal" layer of storage and CPU virtualization
Layer 2 - Application virtualization - This is when you use web services or APIs to provide a specific function or capability.
Layer 3 - Process virtualization - This is when you string web services and APIs together to deliver value (function or capability) to an end user
Different infrastructure terms can then be used to describe how these layers are put together:

Layer 1 is grid computing, utility computing or IaaS. The specific descriptive term is a function of the business model used to deliver the capability
Layer 1 delivered with layer 2 is PaaS. A developer uses the platform services or APIs to create value for an end user
Layer 1 delivered with a software application is SaaS
When Layer 2 and Layer 3 are designed with web services and layered on top of a hardware infrastructure (virtualized or not), you have a Service Oriented Architecture
Layer 1, 2 and 3 delivered with services and/or APIs already organized in workflows and delivering value to an end user is Cloud Computing.

@ Cloud Pyramid
Feel free to use the analogy. My original post is at [http://blog.gogrid.com/2008/06/24/the-cloud-pyramid/] .

-Michael

Consumers of cloud computing services purchase computing capacity on-demand and are not generally concerned with the underlying technologies used to achieve the increase in server capability.

Useful typology indeed. I am going to use this if I may in training...