I have been trying out the 'inbox zero' approach in my gmail account for the past month and I am happy with it. I had archived about 9200 mails from my inbox when I started and have kept it clean ever since. Whereas before I used to keep track of important mails by starring them I now use the GTDInbox Firefox extension that extends GMail's interface and allows one to attach multiple labels to mails in accordance with Getting Things Done terminology.
On arrival a mail is read, labeled if important and then immediately archived. For TODO items that are not originating in mail exchanges with someone else I send a personal message, which is one of the features added by GTDInbox.
I have also started using k,j,r,],x,y and other GMail keyboard shortcuts which help avoiding the mouse most of the time.
It's nice to know that projects, next actions and references are somewhere where I cannot easily see them, as opposed to having them staring at me from the inbox page and making me feel guilty :)
I wish there was a similarly useful Firefox extension for Getting Things Undone.