Since GLT11 where a GNU Emacs session turned into an open show and tell I am aware of the existance of Org-mode. As you might already know, I was using GNU Emacs and later on switched to (g)vim. Just because of Org-mode, I am now using GNU Emacs again. And I do think that it's worth to learn GNU Emacs just because Org-mode.
So what is this Org-mode anyway and how can it help you?
Org-mode is hard to explain. First of all, it's a cool Emacs mode (I often refer to it as a tool box) where you can use few or a very large set of features to help you organize your stuff.
You can use it as a quick method to outline your ideas, manage your tasks in a basic or even very advanced way, log your time spent on certain tasks, structure texts, create presentations, easily write and modify tables, create cool spreadsheets in text files, use it as a personal Wiki, track your habits and goals, tag information chunks, capture ideas very fast, export and import to and from many different formats (HTML, LaTeX, PDF, ...), easily write source code documentation, and much much more.
So it depends on /your requirements/ how much and what of Org-mode suits you. The result is always the same: plain text file(s). Each and every thing in Org-mode results in a simple text file containing all of your information. No data base, no complex programming language needed. For example you can use Org-mode as an implementation of GTD which is a method defined by David Allen.
If you want to have a short introduction to Org-mode and some of its features, watch the Google Tech Talk by Carsten Dominik which is the person who started Org-mode in the first place. But there are a lot of shorter Org-mode demos available too.
My personal goal is to manage my todos using Org-mode because Org-mode provide features like simple dependencies between tasks and even advanced ones, separation between scheduled and deadline datestamps, tagging of tasks, logging of task state changes, and a very cool mechanism to derive agenda views from my Org-mode files.
If you are interested in those things, you might want to read a detailed example of another guy. But sooner or later you are going to print out the very good 200 page documentation of the basic features and browse through its powerful featureset.
I also began to set up a system for managing my collection of research publications similar to the system described here.
Unfortunately there are some things that should be better in my opinion. For example the main reason for Org-mode is task and project management. Therefore its calendar features are only rudimentary. So Org-mode is not a replacement of my good old system using a PalmOS device and JPilot as my desktop calendar.
But there are clear advantages of an additional calendar (agenda view) in Org-mode! Since the calendar view is being /derived/ from the Org-mode entries, a time scale is not the (only) mantra being used. You can keep similar things together, depending on /your/ mental system. Repeating tasks are not splitted up (to different days of occurrence), attached information always stay at the tasks. I guess you have to try it by yourself in order to really understand what I was trying to explain here.
Import and export is great! I can derive PDF documents (via LaTeX) and all of my recent blog entries were written in Org-mode and exported to fine HTML to be copied here.
Org-mode is huge! First I wanted to map my task requirements /only/. Then I stumbled over so many cool things that I plan to read the whole manual and decide which feature I want to test and which is not that important for me. Lots of clever guys made lots of clever features I was not aware that I can use to enhace my personal workflows!
Short side note: Since I was using gvim, I tried to use Org-mode within vim. There are some extensions to gvim that provide similar approaches but noe of them worked that well and was that good as the original.
Org-mode is great in your GNU Emacs running on your computer. But since we all are able to live and breath without notebooks, we want to capture things, access task lists (shoppinglists?), and so forth being mobile too.
For you iOS users with iPhones, iPods and things: you're lucky! There is MobileOrg for iPhone and iPod Touch which looks pretty good to me. I did not test it because I do not own an iOS device. I am using an Android phone. And there is MobileOrg for Android which I already tested. Please buy the donate version to support development. The current stage is somewhat beta. So for capture and show task lists it's already good enough. But there is still a lot of development necessary.
Currently there is a small discussion on the mailinglist where another attempt could be promising: redirecting mobile input to a running Emacs session on a server and sending the results back to the mobile device to be visualized. This method would not need the time-consuming re-implemenation of Emacs Org-mode ELISP functionality into Java.
If you are already using GNU Emacs, you simply have to learn and use Org-mode for so many things. It is a very handy and clever help to your digital and not so digital life.
But if you are not using GNU Emacs (yet) and you are looking for an easy to use and yet easy to extend (to more advanced features) system, I recommend you to learn GNU Emacs. Even if Org-mode is the only thing you are going to use GNU Emacs for. But I seriously doubt that this will be the case ;-)