Software-as-a-Service is useful for products that require network connectivity, such as email and instant messaging; just witness the popularity of Gmail and Meebo. Among enterprise customers, ERP/CRM applications hold some degree of promise, like Salesforce.com. So then the question is whether technical computing customers could use SaaS.
The best example I can think of is in offloading hefty workloads to managed servers. This isn’t grid computing as traditionally known, but rather an application that can be called on-demand to perform a very specific task. I believe that in the future, it may be possible to farm heavy number-crunching from Excel or MATLAB to another company’s server on the fly. I’m just waiting for Microsoft to introduce “Excel Services Live.” You heard it here first.