http://www.blender.org/modules.php?op=m ... pic&t=2463
So I post my reply here:
p_vertex_ wrote:... the ability to toggle different sets of layers on and off, where set membership is not exclusive. Sets, in and of themselves, would not be associated with buttons, nor would they need to have shortcuts (although the ability to assign a shortcut would be nice). The problem, as I've described it, is having to toggle multiple groups of layers on and off repeatedly throughout the development of a scene. The solution, as I've proposed it, is the ability to delegate this toggling function to another entity: a set or group. I'm not clear as to why this can't work as an adjunct to the criteria that you've specified:
So we would have layer buttons like now and another kind of buttons for groups of layers. I understand why you want to be able to toggle groups of layers at once. Would be useful, no doubt. But I very much dislike the idea of introducing an additional concept, that is very similiar but not entirely the same as the present. An the extra space needed for buttons exclusive to toggling groups. The need to differentiate the button types.