I'm not sure how much this helps, but: in my own testing exploits, I've found it useful to separate helpers into four kinds:

1.  Inspection helpers (here that would be just "find")
2. Behaviour helpers (we don't seem to have any of those in ember at the moment, but that would be such things as creating a text selection in the UI, or changing the text in a control without triggering any events - it might be that "fillin" is a behaviour helper here, because it's not a proper simulation behaviour. Generally, though, a behaviour helper should be about emulating the way the browser reacts to user input - I've found this necessary for emulating browser behaviour where browsers don't react properly to javascript events like keypress events).
3. Simulation helpers ("click", "keyEvent" seem to be these kinds, except I'm pretty sure they don't fire *all* the user events that a click or a pressing a key do. My simulation helpers for pressing a key tend to include the behaviour as well, so for example, pressing a 'q' key involves triggering three events (keydown, keyup, kepress) and changing the current caret position as well as changing the content of the currently focussed control) Ember's click and keyevent helpers seem to site somewhere between behaviour and simulation... perhaps evented behaviour?
4. Assertion helpers (It seems we haven't enumerated any of these yet, but there are a few... such as "blank", containsInstance, and "not", which make ok() assertions on things).