Definitely not for application state, but for resource state, a FSM can be invaluable. Take for instance something as simple as a blog comment system, where any

Definitely not for application state, but for resource state, a FSM can be invaluable. Take for instance something as simple as a blog comment system, where any administrator needs to be able to transition a "comment" resource into either accepted or rejected states. They also work great for transactional resources like a shopping cart order.