For my day-job, I use Outlook for a lot of things. At home, we have a pad of sticky notes that we use for making grocery lists, shopping lists, and notes of various kinds. It is centrally located and anyone can grab the grocery list if they happen to be going out. I had a freeware To-Do list on my computer at one time, but I stopped using it. I also email myself reminders, from work to home and vice-versa.
I have been mulling this same question over myself the past few days and considered asking a similar question in terms of specifically how do start-ups organize themselves in regards to time, appointments, making sure things get done. I seem to be suddenly on the right track for some of my goals in that regard and wondering if I need more "organization"/structure. So I am looking forward to hearing other ideas on the topic.