1. Being in the zone is good, but you may be functioning mostly on instinct, so the more experience you have, the better results you ll get. By that I mean that it s where that thing called craft helps you. You then have some techniques that you can rely on, and not only your gut feelings.
2. While being in the zone, it's still good to jump out of it and criticize your own work (as in you always have to be your best critic). It s almost as if criticizing yourself should be a reflex, part of your instinct. Sometimes I imagine someone commenting what I do and me trying to defend my work. If I can't defend it well, that means I better look into :)
And I've mentioned that in another comment, but that applies to any work, whether it is considered creative or technical (knowing that there is a big overlap between those). As a person doing films and web app, my thinking is not very different from one to the other.
(Thanks to you for making me think about this)