On April 11th, after months of toying with the idea of setting up a permanent treadmill at my work desk and asking my coworkers if they'd be bothered if I did so, I bought a (relatively cheap) treadmill off of Amazon. On April 16th, the treadmill was delivered. (Shout out to the amazing facilities crew at work, whose only questions were "when would it be convenient to you for us to bring the treadmill to your desk?" and "let us know if you need any help putting it in a vehicle later!")
It's been a little over two weeks of using the treadmill at work now, and I have to say: treadmill desks are awesome!
I had been using a standing desk for months, listening to my body: sitting when I was tired, standing when I was restless. I'd gotten to the point that I was standing most of the time. I think this has helped in my quick transition to the treadmill desk, which obviously doesn't allow for a chair at all. And anyway, I think walking is easier on your feet than standing still, at least for long periods of time.
When my feet really do want a rest, I just take my laptop over to the couch that's just 50 feet away and take a short break.
I am "allowed" the treadmill in an open office floor plan only at my coworkers' good graces. So the first thing I did to the treadmill after turning it on was disable its super-annoying, constant beeping.
Thankfully, the treadmill itself is only minimally noisy. Honestly, I think the tiny fan I bought is noisier than the treadmill. The important point is that no one at work has complained about the treadmill yet. On the contrary, even strangers have wandered over to ask variations on "what the heck is that?" and "how did you get it?" and "can you really type on that thing?" (Answers: a treadmill! with money! and yes, just as fast as before.)
The treadmill's computer console does not disconnect entirely, but its cords are long enough that I can set it down on my old standing desk and get it out of the way. The handlebars are welded to the base frame, and as such are not (easily ;)) removed. But they are horizontal enough that a $6 wooden shelf from Lowe's is extremely stable plopped across them. I thought I would have to somehow secure the plank to the handlebars, but so far it's shown no inclination to move and I haven't bothered.
From the photo of the treadmill's console hiding on the old standing desk, you might think that it's really inconvenient to use. Luckily, this treadmill model also has redundant controls at the ends of the handlebars, which stick out well beyond my shelf "desk". So I only need to reach across the desk to push the console buttons when I want to reset the statistics mid-day (which I almost never care enough to do; my Fitbit tracks all the stats I want).
As for the health benefits... Make no mistake, walking at a speed that doesn't interfere with creative computer work (ie, 1–1.5 mph) is not an aerobic workout. I barely break a sweat when I walk for an hour straight. But what it is better than is sitting my butt in a chair 8 hours a day, only to come home and sit on the couch until bedtime.
The treadmill does not replace my actual workout/gym time. But it does replace a large chunk of my 100% sedentary time that I otherwise couldn't get away from, given my job as a programmer.
Ask me how I feel about my treaddesk setup in two months... But after two weeks, I'm just mad I didn't decide to do this sooner!