David and others have mentioned PersonalBrain as a potential useful tool. I've managed to implement GTD using a combination of Outlook and PersonalBrain.

I've started a thread on the PersonalBrain site for anyone interested. I'll answer any questions, but only in the one space.

Here's the content of the original post.

For those who are interested I now have a working integration of PersonalBrain and David Allen's Getting Things Done methodology. In truth I don't know where to begin explaining how it works - it's all in my brain! However I'm happy to answer any questions from fellow GTD'rs.

The basic components are:

1. Next Actions and contexts are tracked in Outlook
2. Projects and Someday/Maybe items are tracked in PersonalBrain. This allows me to get much better context for a Project. Projects get linked to a concept, GTD Horizons of Focus and other goal related items as appropriate.
It's very powerful and given me new insights into my goals and horizons of focus.

Cheers,

David