I've seen a huge personal impact adopting principles from David Allen's Getting Things Done methodology, which in some ways is simply a checklist management system. As others have mentioned, it's not just preventing me from forgetting to do things. Capturing my thoughts and intentions externally reduces stress and frees my mind to have more new thoughts. My creativity has skyrocketed since I started writing down every project/product idea I have, and adding to them over time. Currently using Trello (which works great for this), but eventually I'd like to switch to something open source or make my own system tailored to my needs.