It's about as good as any multi-tasking. If you're really good, you can get away with it looking productive, but studies have show managing a single task at a time works best. You will get a better machine/body interface if you're not trying to walk around. You could argue that standing is slightly more healthy than sitting, but the counter argument would be that maintaining any position for prolonged periods is bad for you.
I think we're moving toward a "Ghost in the Shell" machine interface where our electronics wrap around us. Just look at the Mad Catz Gaming Mouse, or the mind controlled gimmick electronics. We're working on interfaces that work around a sedentary body, and eventually we'll replace the parts of the body that have a problem with sedentary behavior.