When thinking about your enterprise software environment, how much of what you use is in support of your business versus that which is core to your business? If you think about it, a lot of what your IT department spends its time with in a given day are merely tools to complete the job, and not exactly core to the practice. Yes, you need some kind of external mail system. Yes, you need to serve files. Yes, you need a website (or several). But do you have to OWN them?
Bill Snyder reports in an article from CIO magazine that first, it matters which decision you're considering. For instance, the way Salesforce.com sells their software as a service (SAAS) and applications platform is very different from how IBM sells their data mashups, as well as their High Performance On Demand products.
In the article, Barney Pell from Powerset gives some suggestions for how people should consider planning out their first steps into cloud computing, by examining which servers and applications are used only occasionally (or at least not all the time), and seeing which might make for a great pilot of the practice.
There are many decisions to be made, but the benefits are improved flexibility at a lower cost. Have you considered shifting some of your applications into the cloud? Check out Bill Snyder's article here.