I've been using Unity's component based design, and the biggest problem I've faced is how to control an object's( not component's ) state.
The problem is, some components must act differently based on the object's state. However, checking an object's state within a non-specific component( imagine we have a "DamageEnemyComponent" ) won't work at all because it makes assumptions about the object it's attached to.
The alternative is to make each component perform one, and only one function. The components are then disabled/enabled or added/removed depending on the object's state( probably managed by a more specific component. )
Imagine we have a "Boomerang" object. Assume it has only two states; idle( being held by the player ) and firing. In the idle state, the boomerang would have very few components, because we don't want it to interact with the world while it's simply being held. It may have components to listen for a "throw", though. Once it is thrown, some state manager on the object needs to update the object to have components for moving, damaging enemies, maybe picking up items etc. When the boomerang is back in the hands of the player, it's component list would need to be restored. This would work, but it would basically be building a new game object for each state, which is incredibly tedious and messy without Unity's editor. Not to mention the inheritance and interfaces can't be used well here( since the state specific components will be built into the state manager script. )
I can't see a way to control state using Unity's components. How is this usually done? It feels as if Unity should provide a way to build different states in the editor, much like building an object.