I've certainly been in The Zone before:
Sometimes, you just have one of those days. One of those days where you manage to find flow, and stay in it. One of those days where you move from test, to code, back to test, back to code with ease.
But what about those days you feel like you're pounding your head against the wall. No matter what you do or try it just doesn't work. Or you're trying to fix a bug and just can't seem to find the problem. And when you do, it was sooo simple - ARRRGGHHH! I battled with The Wall all day yesterday writing installation scripts for my current project. I was lucky enough to get it all working by the end of the day, but I think I scared the bejeezus out of my cat a time or two.