AppFog comes handy when building a prototype. A typical prototype that requires a quick web service deployment with a database layer is where I had used AppFog. It isn't used across the organization. I have also used AppFog as a student at my university. Our team used it for bringing our projects to the cloud.
Primarily because it used to have a good free tier earlier, which it does not anymore. It's simple, and things are available to use. Compared to it's competitors, it does has less features, but that kind of acts in its favor. That adds to the simplicity, and ease of use for a new user.