lyes wrote: "...you can add transparent picture with a bit off color in the hole..."

Yep, that's what I'd been doing in Rhino. I set the ground plane material slightly transparent to control the "reflection" amount of the mirrored objects. But I hadn't thought to use an image of the sky beneath it. It's a nice effect. But it's hard to find good pictures for interior ceilings. I will need to walk around with camera and take pictures like a tourist... :)

And it could be taken one step further to use an alpha for simulating puddles of water on the ground plane too... :)