I agree that this is really what a lot of people are probably discussing -- how they feel, whether they are in the zone. The interesting question is whether it really corresponds to getting stuff done. Solving interesting problems in new ways often puts me in that zone, but I'm not clear that such solutions necessarily buys the organization more.
I usually feel like I've been productive if I spent most of the day in the zone - but the truth is, that doesn't always move things in the right direction. For instance, I might suddenly obsess over some little visual detail that I want to get just perfect and end up spending an entire day on it. At the time it feels right - but looking back later when the project is behind schedule and everyone's in crunch mode, I have to wonder if that was really a productive day or not...
