I found that emptying my inbox and making a determination to keep it empty - that is, to deal with every piece of incoming email immediately and either do it, bin it, file it, delegate it or task it was the most useful part of the GTD process for me. Just this simple thing solved 95% of my productivity problems.

Because that part worked so well, I have been slow to implement other parts of the methodology (the filing, the project lists, the weekly review) even though I think they're a great idea. I'm currently in the middle of a huge "virtual shelf" processing phase, as my computer "shelves" (across three computers) was the worst mess in my life.