Currently playing with Foresight, a Getting Things done plugin for Outlook.
It’s now free, and fixes the traditional problem with the Outlook task list of not being able to handle anything beyound the most simple of projects. Watch this blog for how it goes.
Paul Browne 
Hi Paul,
I’ve been practicing GTD for about 10 months and now am incorporating the practice slowly into our company as they way we manage projects.
We have a mix of platforms and have not yet found a cross platform tool that will work for us. I use a Mac and have tried iGTD (http://www.igtd.pl) and Omnifocus. iGTD I felt was the best implementation but as it’s developer moved to Cultured Code (http://culturedcode.com/) and it had no iPhone App to allow me to sync and be mobile I moved to ‘Things’.
I am now very happy with Things and use it’s tags functionality to easily implement contexts and it’s projects functionality and ‘Today’ list are brilliantly simple – it also has a nice UI that makes using it a treat every day!
We are experimenting with ideas here to possibly produce an open source module for SugarCRM to provide an effective ‘groupware’ implementation of GTD … but we need to examine resources required of collaborate with others.
I’m also (more immediately) looking for other GTD practitioners in Ireland to get a network together to support and encourage each other – I see great synergy between GTD and XP/other agile approaches in that they both have honest and practical bite-size planning at their heart.
Graham