It’s roughly equivalent to giving someone a car in which the steering wheel has been replaced by a joystick. Not only do you need to learn how to steer with a joystick, but all of the controls formerly attached to the steering column are now scattered in various spots on the dashboard. The wiper control is a lever above the radio, the high beam lights are a switch on the rearview mirror, the turn signal is a set of buttons under the speedometer, and the cruise control is a dial hidden inside the ashtray. Oh, and you honk the horn by bouncing up and down in your seat. —
Michael Mace, on the issue of how Windows 8 is not the easiest to use if you have spent the last x years on traditional “Start” menu based Windows.
Does this not sound rather like an analogy for users of Assistive Technology? Where even small changes; say a moved switch, a sticky rollerball, a joystick no longer in the same place or the debounce on the keyboard being changed - causes equal amounts of “annoyance”.
In short, if you change something think hard and long about it and keep it that way for as long as possible. Otherwise you may end up making your users feel like they are driving clown cars when they want to be doing far more important things like communicating.