From the 37 signals article, it seems as if to be 'in the flow' or 'on a roll' one must be completely focused on a task at hand. Now that sounds like a good state to be in when one is actually working on one project or another. I've been that way myself on many occasions. However, it also tends to lend to tunnel-vision, IMHO. Because I am so focused on the task at hand, I tend to lose awareness of everything but the task or project. When I am running 'in the zone', all I think about is running; when I am driving 'in the flow', my main focus is the road and the traffic around me; when I am mudding drywall and 'on a roll', my work is my primary focus. The outside world does not intrude, unless it relates to what I am doing. Again, it gives me great focus when I have a set task to accomplish, but if there is a non-task related intrusion it tends to set off my rhythem. Also, if the unexpected comes up while you are 'on a roll', well that's when you run into a
Brick Wall. That's why I don't have my cell phone on when I'm driving. Also, when I am between projects, I may not necessarily have a focus, so being 'in the flow' would be counter-productinve IMHO. Then, I need to have a clear mind that will go in any direction as needed, so I can determine what needs to be done next, otherwise I could wind up 'in the flow' grooming my cat for a few hours, resulting in a very happy cat, but not much else.