I posted something awhile back about the "[http://www.sheldonrampton.com/node/109 Stairmaster desk]" that set up so I could work on my computer from my Stairmaster rather than sitting down.
Originally, the Stairmaster desk was just a piece of cardboard folded into the shape I wanted. As I expected, the cardboard didn't hold up very long, so I had Chris Breunig (the husband of my wife's niece, who works as builder) make me a more permanent solution out of wood. Here are some photos.
The wooden wedge by itself, sitting within my plastic book rack atop the Stairmaster's control panel.
The completed item, with the top from a [http://www.stacksandstacks.com/html/762_computer-lap-desk-padded-wrist-… computer lap desk] attached to the wood. This gives me a larger surface, with enough room for my cell phone, a pen, or other small small items in addition to my laptop. Also, the padded wrist rest from the lap desk provides some extra stability to keep the laptop from sliding around, reducing the risk that it will fall off and get damaged.
Here's another shot.
Unfortunately, the basement where I keep the Stairmaster is pretty chilly during the winter months, so I'm not planning to use it as a desk until the weather warms up again. Using the Stairmaster for regular exercise is still fine. (Once I work up a sweat, I don't notice the cold.) The Stairmaster desk, however, is intended only for use while doing very, very light exercise, which isn't enough to stay warm.
I suppose eventually I'd like to figure out a treadmill solution for my home office that I can use year-round, but this is at least a step in the right direction.