One difficult I had with such schemes was that "Read first chapter of X" doesn't map to any particular locale. I could read it at the library, or in my office, or at home, or while sitting in a park.

In that respect, it's like the @calls context, which is based on particular physical activity.

Except my list of things to read is either too long or too silly. Do I want to have "Read chapter 1 of X" followed by new NAs for each chapter? If not, then do you put "Read X" as a single NA even though it'll take you seven hours to complete?

For me one of the main difficulties of mapping GTD onto life in the humanities. I imagine it's difficult for artists as well: there's a certain level of administrative gunk that will benefit from GTD, but at some point your only task is to sit down and paint the damn picture. Somehow "@studio: paint portrait's left ear" is both hurtfully distracting and patently absurd.

I only mention it (again) because it took me a long time, a lot of wasted effort, and a lot of anguish to discover that for my work, GTD is only an 80% solution. The (large) number of things it adds are of considerable worth, but trying to get it to fit the last 20% is destructive and frustrating.

I'll bet that most academics who use GTD are in the sciences, where the varied tasks of designing and implementing experiments, working with others in a lab, or working with abstract data provide a sufficient diversity of tasks. In the humanities and (perhaps some of) the social sciences, follow David Allen's advice and pick up the tricks that will give you the biggest boost (and don't worry about ignoring the rest).

Since the OP didn't state her (his?) field, we're left to guess until given more info. Once she tells us that she's a computer scientist, I'll shut up and wonder what took her so long.