Getting Things Done (GTD) is an organizational method created by David Allen, described in a book of the same name. The Getting Things Done method rests on the principle that a person needs to move tasks out of the mind by recording them externally. That way, the mind is freed from the job of remembering everything that needs to be done, and can concentrate on actually performing those tasks.
I read the book and love it. It balances between theoretical reasoning and practical attitudes. It says explicitly that it is not about a computer program, or a special type of note book. You are free to use any system you want. Webmail, Outlook, notebook, folders, color tags… you decide. But the book is smart enough to give you hints about using them, just for the sake of starting soon and being practical.
It at least opens the mind for being more productive in our ordinary life. Just dont go crazy to think about it all the time because, paradoxically, it can be really nonproductive.
PS: I recommend you to strive to use for 3 months, forcing yourself. Its easy to start but because it requires a new mindset, keeping using the system harder and harder with time.