If you didn't continously supply the yeast with some oxygen through stirring, intermittent shaking would be more efiicient. And I think Braukaiser shoved that vigorous stirring on a plate without capping is the most efficient way. You get less yeast growth if you use an airlock.
Shearing of the yeast is a myth. As you say, you would have to spin the magnet much faster than we do in order to damage the yeast.
I'm not sure the oxygen will help you much if the energy reserves of the yeast are depleted, which is what is happening if you spin for too long. (But I've earned my living teaching litterature, history and philosophy, not real science, sadly. So my knowledge about these matters aren't too deep. I've tried to understand a little, though
.)
I'm sorry, guys; it's nice to know what you're doing, but what I wanted was some solid science based information about when to take the starter off the stir plate. I haven't been able to find any, and I'm at a loss to understand why all those people out there haven't cried out for this in unison
. I can't be the only one who have felt the need for something a little more solid to base my actions on?