Many thanks to Yvotchka for Tweeting me this very interesting article, The Power of 1 by Time Management Ninja. The gist is, have only one of each tool: one address book, one planner/ calendar, one to-do list, and one notebook. I appreciate that the point is simplicity, and I do agree that having your information in too many places leads to confusion (which I have certainly experienced).
In my opinion, the only way this idea will work is if you keep all of your information electronically so that you have access to it on your computer and your hand-held device. But for those of us who are paper-only (more or less), we cannot carry all of our information with us all the time so we have to have it in separate bits.
I'm not normally argumentative, but I want to dispute each of these points.
Address book: TMN's solution is to keep all your addresses and contacts electronically. I don't do this, I keep them all on paper. I definitely do not want or need every address of everyone I know with me all the time. My solution, and what many people do, is to have a master address book that stays home (with everyone's address I know), and emergency contacts and frequently used info in my planner that I carry with me. I find this to be entirely reasonable.
Calendar: Again, unless you use an electronic calendar, it's not always convenient to have only one single calendar. Despite the fact that I have gazillions of planners, I only ever use one weekly planner at a time, which is my master planner. Everything goes into my weekly planner. Because I have a family, I also have a wall calendar so that everybody else can see what's going on too. I update the wall calendar from my master weekly planner. I know plenty of people who use Outlook or similar at work, and a Filofax or other planner for their personal use. As long as you synch appointments, you'll be fine. You will run into problems if you have a calendar at home that you write things in, a calendar at work that you write other things in, and a planner in your pocket to write things in when you're out and about. No synching = big trouble.
To Do List: I don't know how it's possible for anyone to have only one To Do List, and I really do not think it's a good idea. I think TMN's point is for those folks who tend to write things on sticky notes everywhere. And in that case, I agree you are better off having one master list to capture all those tasks. But I just can't imagine having one big to-do list full of home, work, school, personal, and whatever else types of tasks. I would get completely overwhelmed and would not be able to prioritize at all. Even Getting Sh-t Done, which is the most elegantly simple task management system I've heard of, has a Master List and Today's List. I like separate categorized lists, or projects with steps, to help me prioritize and know what to do next.
Notebook: Here is where I most strongly disagree. Maybe TMN means having only one notebook as your inbox? Then later you can move that information to the appropriate location. If I used only one notebook for everything it would be a big jumbled mess without linearity and I'd be completely lost. I told Yvotchka I like to use notebooks for topics, similar to how I had a separate notebook for each class in school and university. I really like Charlie Gilkey's notebook system. His is proof that a system doesn't need to be elaborate to be effective.
So anyway, I don't mean this post in any way to slam Time Management Ninja. Some people do work better with only one tool each. But for many of us, I think compartmentalization is the key to organization.