My doctor suggested I use a treadmill desk after I had a bad episode of nerve pinch in my back and sciatica during a crunch time. I bought one and loved it. There were some minor practical issues using it at work, but none related to over-walking or anything like that. Personally, I doubt it's possible to over-walk at work with a treadmill desk, like the author of the article implied.
I'm a runner as well, and I've tried a standing desk (as opposed to a walking desk) a few times, and while some people love it, my feet start to hurt very quickly when I just stand (after 10-15 minutes). Even if I use running shoes and a soft standing mat, and even if I shift my feet & weight a lot (or not). I don't have that problem at all while walking at a treadmill desk.