One of the statements in the David Allen book is that you should use a system that you find fun to use, because that will make it easier to stick to it. To me, it is always fun to try out new things, and abandon old stuff in favor of new software.
My way to stick to my GTD lists is that I once in a while change the system with which I keep track of the lists. To find a new, shiny peace of software, keeps me interested in using the lists, which is of vital importance for the success of your GTD system.
Systems I have used so far:
- The todo application and memos of my Palm Tungsten T3
- Microsoft Outlook in combination with a HP ipaq 214. (Note: I found this setup extremely inconvenient. In my opinion, Outlook Mobile is not a user-friendly application.)
- AbstractSpoon hierarchical todolist
- Home-made GTD tracking software. This worked for a while, but wasn't really a good idea in the long run since you have to solve issues and create additional features all by yourself ;)
- Remember The Milk
- bLADE wiki. It is a personal wiki that works on Windows Mobile and on my desktop. It has no built-in support for GTD because it is a plain wiki. But if you take some time to arrange things the way you like it best, it is a very pleasant system to work with. At least I am very pleased so far. And my wife is too.
- [Update] Because I bought an HTC Desire Android device lately, I created my own Personal Wiki for Android which I'm using now.
(The image is a GTD wallpaper from http://anabubula.com/)