According to the NYtimes, 355 Treadmill Desks have been sold nationwide in 2008 and I would expect that number to jump dramatically. The big companies that are currently purchasing these treadmill desks for their employees can afford the high price tag on Dr. James Levine's product, but what about the average joe's who want to shed some weight while working.
You can attempt to build your own treadmill desk if you want like this guy (http://www.bookofjoe.com/2007/10/treadmill-works.html) but most of the build it yourself desks I have seen are ridiculously ugly and you would never want one in your home. I love for my workspace to be inspiring. The treadmill idea is inspiring, but the idea of a pitiful little desk, or a big ugly one will not inspire me much.
One of the great things about the treadmill desk is that standing, walking, and the blood flow has a great affect on your bodies energy level.. While you would think that sitting down would keep your energy up, it actually drains your body and you fall into the zombie mode. When your walking, your energy level sores and your creativity also flourishes.