I’ve stopped using the term “Cloud Computing” except when referring to the general trend. I use SaaS, IaaS and PaaS so that I say exactly what I mean. As a technical person this helps me keep my conversation succinct and focused.
SaaS: Software as a Service: Salesforce.com, Google Apps, etc.
PaaS: Platform as a Service: Google App Engine and similar systems.
IaaS: Infrastructure as a Service: Amazon EC2, Eucalyptus, etc.
Or, if you want a way to remember it easier:
SaaS: It’s a web site!
PaaS: It’s a framework!
IaaS: It’s a VM!
“Cloud” is what marketing and non-technical people use. I’m ok with that.