In my experience, GTD is overkill and managing things that way is a time consuming task in itself. I converged on something simpler: I have four lists. One that contains everything that absolutely needs to be done. Then there is a list for things that can be done but are not essential. This list is a pretty amazing collection of ideas and when I have some time left, I pick an item that looks appealing in that situation. Then there is a reading list and a list for completed tasks. All lists are stored in one org-mode file (along with tons of other things). The list with important stuff is frighteningly long. At first this bothered me but I got used to it. Now I see it as a resources. There is always something on that list that I'd like to work on. Once a week I go through this list and move some items to the non-essential list. If something stayed long enough on the important list and nothing bad happened, it's probably not important.
I love GTD because it has the least amount of friction possible in any system that would actually work for me. I spend seconds at a time adding projects to my system (OmniFocus FTW), maybe 20 minutes a week sorting new projects into larger projects and contexts, and almost zero time deciding what I need to be working on given my location and available resources.
GTD seems like it has a lot of overhead, but I kept at it long enough that it became the way I think about work. It's practically invisible to me now.
Sounds similar to the 4-quadrant system of important / not important and urgent / not urgent. I forget the name of that, but it always seemed like a decent idea for guiding prioritization (if used as a hard rule, it would inevitably lead to not-urgent-but-important things never getting done).
