Ed Sims on DIY in the Enterprise got me thinking about this services thing from the other angles again.
Your IT department can probably block the installation of client applications, but they're going to have a harder time taking away people's web browsers. Subscribing to Software as a Service (SaaS) is one way of dealing with slow/unreponsive/restrictive CIO orgs (at least for browser based apps). I have been several places where local installs were prohibited- even for developers. It makes it tough to try out new tools. Which makes it tough to improve things. Which makes it tough to innovate, et cetera.
Obviously, there are good security and stability reasons for not letting everyone install whatever they want. But I have found that organizations who make that restriction universally lack a way to get software X quickly approved on a trial basis. I realize getting a corporate lawyer to read an EULA is probably a good idea, but it shouldn't be a pre-req to updating software to fix bugs.
One thing I don't get is why so many SaaS have to be ONLY services. A lot of enterprises I have worked with would like to take the applications that are being run in SaaS fashion and bring them behind inside the firewall for secure/managed use. A lot of people are developing applications where something would be better off as a component than a service. This is particularly an issue with depending on SaaS startups- you don't want to wake up and find they've run out of cash and you can't run your business. I still support an old application I wrote using a Lotus Notes software component from a company that was acquired by a competitor who discontinued the product in 1998. If this was offered as a service- my app would have been dead for years.
I like the idea of corporate/government users using SaaS in a non-central-committee fashion (rogue user alert), but the SaaS vendors should then make a behind-the-firewall product available so that it can be transitioned to a controlled environment.
I think there is a definite analogy to mapping services. Sure, for 99.999% percent of situations, it's probably cool to depend on Google to provide continuous service for Google Earth Pro. However, if you have your own massive proprietary dataset, need some local control over things, etc- you are going to want to go to Enterprise and bring it behind the firewall. They even offer a hybrid solution- to layer your vectors on top of their imagery/terrain. Just offering any one of these three things probably would be a non-starter, but they've definitely garnered their reputation from the awesome quality of their SaaS.