After ~2 years of having a manual treadmill at my desk, which functioned as a standing desk because walking was effortful and standing was not, I bought a powered treadmill and just finished installing it and mounting my monitor. Initial tests are very encouraging; as expected, walking is mindless and doesn't interfere at all with reading / browsing the internet.

Typing and using the mouse are a bit of a pain, mostly because I don't have a flat surface for those at the appropriate height. Am considering going with a split keyboard / trackball mouse instead.