I've done it, gotten my physical inbox and Gmail inbox to zero.
It was easy - you just move everything elsewhere ;-)
The truth is somewhere in between real empty inboxes and simply moving stuff.
Let me back up: I'm planning on a fairly strict implementation of Getting Things Done for my new job. Rereading the book. Sorting things around the house. Getting my Gmail inbox to zero.
In some ways, the Gmail wasn't too hard. I had about 100 threads. I answered those I could in 2 minutes or less. (Some of you got some of those unimpressive emails ;-) I deleted a lot. I labeled a lot '*maybe' and archived them. And I starred and archived a lot of them. Bingo.
And I've kept it up through the day. She's still empty.
And I sorted some physical stuff I've been meaning to process for a long time. I didn't do a complete collection like Allen advocates. I created a box of stuff to just put in the garage for now (extra USB cables and such) and a box of papers I just don't want to process right now. Maybe the 'open loops' will psychically leach me, but I don't think so
There are a lot of ways I'm not doing pure GTD, but they seem like more peripheral issues (like buying a labeler). I fully intend to get everything for my new job into a system I can trust, and many other things besides.
Got a few more piles to process and relocate tomorrow, but I think I've made a really good start. I guess time will tell...