I was a little late twigging the implications of Gmail’s recently announced IMAP support, but it really is brilliant for GTD-ers.
What is IMAP for Gmail?
In a nutshell, it takes messages you’ve labelled, and allows you to use them in other (email) clients; with labels mapping to folders.
So, P/GTDInbox will map to the folder GTDInbox, which would be a sub folder of P.
And, S/Next Action will map to folder Next Action, which would be a sub folder of S.
Any changes you make, by moving messages between folders, are then perfectly synchronised next time you log into Gmail.
Why is this Great?
First & foremost, it allows you to retrieve/manipulate your tasks using your favourite email client (e.g. Thunderbird); allowing you to take advantage of GTD email features with your regular desktop software.
This is particularly useful when the email client is on a mobile device, like the iPhone, allowing you to access your tasks on the road.
It also allows developers to create specialised (possibly GTD based) software that uses the messages/tasks you have in Gmail as the database. So, in the future you may do 90% of your (email related) task management within Gmail, but use 3rd party tools to either work with it on other devices (e.g. PDA), or to use specialist functionality.
In short, IMAP - while not an instantly beneficial feature - makes GTDInbox & Gmail much more capable as a ‘base’ system that other software can hook into & extend… meaning more efficient/available task management!

Frank Carey Says:
November 16th, 2007 at 4:50 pm
Hey, just wanted to say thanks. I haven’t used it yet, but I’m excitedly waiting for the new release. Kudos
Bryan Says:
November 27th, 2007 at 9:31 am
The gmail extension was great; unfortunately, it doesn’t work with the “new and improved” gmail interface. It does work with the classic interface.
Any plans to provide a version for the new interface?
Andy Says:
November 27th, 2007 at 9:34 am
@Bryan… You’ll be pleased to know GTDInbox v2 will only work with the new UI
Stephen Hultquist Says:
November 29th, 2007 at 9:28 pm
Andy, First, thanks for GTDinbox. It made Gmail usable as a GTD interface!
I have moved to the new Gmail, though, and also use Gmail from my iPhone and Mac Mail, so the changes of v2 that make it compatible with IMAP usage will also be wonderful.
Thanks, again!