Chance are you are already doing it. Unfortunately, the S+S message has been a bit garbled in the mainstream media. The press really does like to create a "MS vs. Google vs. Everybody" style theme. I guess who doesn't love a good fight right? But the idea of S+S has been around for a while and is nothing new. It is not Microsoft's answer to "fight Google" and it is not Windows Live. So what is it? Let's start by defining two of the most often confused terms with S+S first, SaaS and SoA.
SaaS = Software as a Service. Runs in "the cloud", there is no local desktop client to access it's interface out of web browsers. Usually provides an API that you the developer can access via Web Services or Plain Old XML (POX). SaaS describes the way your users will be accessing your application.
SoA = Service Orientated Architecture. This is how you build your application on the backend to enable your services. The basic idea is to create loosely coupled systems out of many tightly coupled ones. This interoperability is most commonly done via such technologies as Web Services and often involves different platforms entirely (Mainframe connecting with Java connecting with .NET.) SoA describes the way you have built your architecture.
S+S = is about choice in how you access your service and choice in how you host your service. You can still access the services via a browser (just like SaaS) you just have the added benefit of accessing your services in more ways. Typically, this is software running on your desktop or on your mobile device but not limited to. Another idea behind how Microsoft is doing S+S is choice of how you will host these services. You can host them on a server in your local infrastructure, via a third party vendor, or even via Microsoft's new data centers. Again, you are probably already doing this. Microsoft Exchange via Outlook is a good example of this. You can run Outlook on a windows desktop, in a mobile browser, and in a web browser. All connecting to the same backend e-mail service. You company's e-mail system is probably hosted in an onsite datacenter, via a third party or through Microsoft. You have probably seen in the news many traditional SaaS companies now offering "desktop clients." Regardless of the technology to enable this desktop client (some of them use web technologies to bring it to the desktop outside a typical browser) and as much as they probably do not want to admit it - this is S+S. S+S is hard to ignore. The demand is there, users want choice in how they access your system. Companies want choice in how they host that system. Microsoft's S+S platform enables that. S+S describes the way your users will be accessing your application.