I have found it useful to add autocomplete=off to the <form> tag in form_helper. It might be helpful to add this as an option in app/config/config.php. Adding into the Settings page might also be useful.

I considered adding it to individual fields where autocomplete is not very helpful - quantity, price, discount, reference no, telephone, and so forth - but that's a lot of places and hard to control.

And, there is no chance most people could agree on which should or should not be disabled!

So, for me at least, on/off systemwide seems a good compromise. And a really easy add.