Haven't considered vertical layering yet, except that I definitely intend to grow lower perennials under the shade of any/all fruit trees. The sun here is so harsh in the summer, it's a miracle that anything survives.
*I* think running grapes up a tree would be okay, as grapevines don't tend to be constrictive or parasitic. I would, however, be concerned about the vines not getting enough sun down under a tree, but I'm far from a grape expert.
