The paradox is that if you write your own chart, that will help you memorize, but if you play off someone else's chart, it will hurt your ability to memorize. I say get off the paper as soon as possible or you won't be able to memorize. This is on a per-song basis, i.e. there might be one song that you look at the paper too much for, and before you know it you can't get away from it. I do anything to remember a chord progression, including making anagrams from the root notes. If you need to glance to remember a specific chord or progression, do so after you try to get through it without.
