Jean-Philippe Daigle Says:
February 1st, 2007 at 8:51 pm
The problem with a combined start/stop button is that many devices fail to provide proper feedback that the keypress has registered.
If there’s significant lag between the keypress and the action it is supposed to initiate, and no immediate feedback, the frustrated user pushes again, thus reverting the state to whatever it was before the interaction began. Discrete start/stop buttons, on the other hand, are idempotent and can afford multiple presses.
Concrete examples (since you asked for some): This happens to me several times a week with my TomTom Go car-mounted GPS and the Motorola RAZR phone. Each of these devices has a single button for on/off, and requires holding it to invert the state of the device, but in both cases, there’s no feedback whatsoever for a few seconds.
Happily, more than a year after the TomTom Go 700 has been superceded by better models, TomTom is still showing commitment to its customers with updates! With the latest software upgrade, they've fixed this little issue. Now, instead of just sitting there silently during boot, the screen's backlight is powered on immediately while the unit wakes up. Granted, it's a subtle piece of feedback, but it works - I no longer power it off with an unnecessary second press.