I've just started trying to start implementing GTD and have set up a system in Outlook where I can move emails to a number of next action folders. This has helped me keep the number of emails in my Inbox down to a manageable number (usually less than 50 and I have been able to get it down to 0 at least once or twice a week). I've set up @todo, @review, and @waitingfor. I'm having trouble trying to create clear boundaries between what goes into the @todo and @review folders. In my mind, @todo are emails that I have to respond to, or contain some action I need to do that will take more than 2 minutes (but usually not much more than 10 - 15 minutes). I have tried to use the @review to keep emails that usually contain documents that I need to review (the only action needed for most of these is reviewing the document). The @todo items tend to have a higher urgency/priority compared to the @review items.
Does this make sense? I'm having trouble staying caught up the @review emails and sometimes, once I start reviewing one of the @review emails, I realize that there are some important things in them that I wished I had reviewed earlier.