Obviously this is the eternal problem of the office worker. As a developer I am sit down almost all of the time as I am straight back on the computer at night until around 12pm most nights.
Whilst novel I think the treadmill idea is obviously no more than an amusement. The dream for me is to have a much more interactive environment to develop software in. It would be nice if you could stand and move virtual components around or build software using virtual components instead of just sitting down and typing. Obviously this would need some sort of higher generation language where more of the problems are abstracted out. It would be interesting if you could build classes like that, then bring up a virtual keyboard or use voice recognition to describe what you want to happen.
I can imagine this working brilliantly whilst pair programming. Two people creating tests, assumptions and building software in a fashion that is almost like a debate crossed with a squash match.
Whilst we aren't as close as I would hope, I don't think we are a million miles away from something like this when you take into account technologies like the kinect and the immersion ideas that Microsoft research are banding about.
One can only hope that this comes before I become so unfit and large that I turn into a Pearl like creature.