Thanks!
Yeah, right now, state that shouldn't be saved (like computed properties) can be added as regular object properties (i.e. not a part of the initialState), and updated by listening for action events.
I've been thinking of ways to make that a little easier, possibly by having "reactions" that execute in response to actions. But I haven't had the need in my own projects yet, and like to err on the side of a smaller API footprint :)