> What's important is consistently moving. That means getting up from the desk every hour for a 5 minute walk or some stretching. Switching between standing and sitting at a desk is a first step in the right direction but really we need to be moving.

Yeah, that's it. At least when it comes to overall health (I'm not sure about back issues).

I did a little bit of research on this theme myself and it seems that the key is to interrupt periods of prolonged sitting with any movement (even walking helps) for any period of time (even 1 minute helps). The more intensive/longer the better, obviously.

See also notes from my web-research at http://mnicky.wikidot.com/healthy-programmer (it's based on the book that got me started on this topic, but e.g. in Section 3 there's some additional reading about benefits of making pauses when sitting for a longer time and similar research).

Btw, using standing desk for prolonged time can be harmful as well, the truth is even more than sitting :) So yes, combine standing and sitting, but stand only for a shorter time (after 30min it starts to have negative effects).