Dion Hinchcliffe really captures the key driver for this new paradigm for software in the enterprise in a recent article. (Hint: it isn't about doing cool, new things to emulate the leading technology companies) He writes, "The motivations for mashups are quite different inside of organizations, where application backlogs and demand for more software that will improve collaboration and productivity are often rampant. If this state of affairs is true, far from having too much software, most enterprises don't have enough to satisfy demand, despite the prevalence of mountains of existing enterprise systems, many of which are underutilized."
In this view, the demand for services and "composite" applications created by end-users is driving this shift. Just as users used to say "Why can't I just do this task as easily as I do it on my PC at home?" in the mid to late 1990's, users today are asking "Why doesn't this work the way my blog works?" or "Why can't we just use one of those free collaboration tools I saw on the web recently?" Enterprise IT can either respond by delivering tools that enable those scenarios for users or they can wait for users to sneak them in through the backdoor.