I have been on a treadmill desk for 4 years now. I highly recommend the standing up part, but not the treadmill part, and probably not for the reason you think. Does walking make it hard to type/think? Not really, not for me. It's the walking posture that's the problem. The real problem with the treadmill is that with your shoulders locked facing forward to type and use the mouse, your walking posture gets really poor. I have hurt my calves several times due to the awkward way I have been walking (not swinging my arms and rotating my shoulders like I should, for example). If you can go hands-free the whole time, it may be great for you, but I am personally switching to a Fluidstance level (ordered it a couple months back, should arrive soon...I hope). Just standing and you tend to "stand hard", leaning on your joints in a way that gets painful. You need to keep shifting your weight around to really make it work well.