Well, I haven't been diagnosed thusly, but there's something related going on. I find sitting still uncomfortable (though I have no problems on focusing per se), and I've realized the point of standing desks is that you can move around a little all the time. Or actually you have to, in order to stay comfortable. If you're one of these people who need to walk around when making a speech or thinking about a problem, you'll love a standing desk. I think I might actually go back to office work now that I realize it's possible to do that without sitting all day. (I've also been a teacher for a few years, and I loved the aspect of not sitting down while doing something relatively geeky -- I actually found my leg muscles getting stronger.)
After hearing a lot about standing desks from friends (and being generally interested about ergonomics, with my Stokke chair for example), I started hacking together one about 2 years ago. I now simply have a coffee table on top of a desk -- I think the monitor could be a little higher, but for keyboarding the height is perfect, with my forearms pretty much horizontal. It took a couple of months to really get used to, and it helps to have some temporary solutions; I still have another sitting desk for paperwork such as math.
(Speaking of keyboards, I've always preferred playing one standing up. It's much better for getting in the mood in live shows, but it also helps my playing when I can move around to the music. So the other standing keyboard is just a logical continuation.)
As per treadmills and exercise bikes, I already made the point of naturally moving around. Frankly, I've never understood either of them in any setting, but it probably depends on where you live. I walk everywhere within my roughly 2-km radius of daily life, and I much prefer doing it in fresh air anyway.
