I've been having some chats in the last few days about how SOA and SaaS work together and how SaaS will actual pan out (as opposed to the hype) and one thing that has become really obvious is that SaaS isn't really SaaS. What I mean is that no-one is talking about buying Software when they buy SaaS, they are looking to buy a Service whether that is a word processor, Salesforce automation, invoicing, accounts or whatever. People are looking to buy a business service which they access, they don't care how that is created, the don't care at all about the technology its just the delivery to them that matters.
SaaS really is about Service as a Service, that is providing a business service whole and in itself in the way that you want. Software as a Service is the IT view, but it isn't IT that is buying SaaS.