hisasith2 - GMail doesn't have folders. It appears to offer an unlimited number of labels, however. Once you apply a label to a message, that label appears in the left hand navigation, just as though it were a folder. However a single email can have multiple labels. This is similar to having one message in multiple folders.
It also appears that a user can set up unlimited rules and have labels automatically applied to incoming email based upon a number of characteristics.
Having explained that, I can see how a person could use this as a GTD system. Simply email your next actions to yourself and apply the appropriate label as context (i.e. @phone, @computer, @home, etc...) This would be great for those items can be done in multiple contexts. I wouldn't do it myself, but I can see how it would work well for the right person. Even the thread views could be used to manage projects -- You could mark completed next actions by reading the email and the whole list of completed next actions would show in a collapsed with the incomplete next actions clearly visible.
I would be interested in hearing deteails from someone that actually tried this. I still wouldn't be likely to convert, but it might give us all some new ideas. I think this is the sort of thing that the original poster had in mind when starting this thread.