People are sometimes surprised at how quickly they adapt to the habit of carrying a notebook--they really start relying on it and very much notice (and curse) the times when there's no paper around to capture an idea or a reminder. I think that, after a week or two, your mind sort of loosens up since you know there's always something there to catch thoughts while they're fresh.

I don't necessarily write very much down while I'm out and about, but if I don't have a small notebook and pen with me, I seem to become obsessed with the fact that I might forget something, so I start making lists in my head, which occupies my brain and keeps me from having creative or otherwise interesting thoughts, I think. Just knowing that I have the ability to write things down frees up my brain to do other, less prosaic things.

Jeremy Wagstaff's LOOSE wire: The Moleskine Report, Part IV