My system is predominantly electronic (other than the stuff that naturally arrives on paper, such as bills), although lately I've discovered that paper is working exceptionally well for the ongoing development-in-progress of a current large project.

This has been a revelation to me lately, as I would normally have rigidly forced myself to capture everything electronically, but I saw that the overhead was too much in this case, and the side-benefit has been a rebirth of my relationship with paper as an adjunct to my electronic system. Fluidity rules the day.

By the way, I still track the overall project and current next action(s) in my usual electronic place for this.