I think a lot of PhD students are finding GTD useful. I'm halfway through mine (we go through them in 3-4 years in the UK, so only a year and a half or so to go). I wonder to what extent this is because most PhD students I know are really thrown in at the deep end - suddenly you've got a lot of independence and it can be really easy to procrastinate, or spend time on the more interesting parts of your work at the expense of getting the results which are actually going to form the backbone of your thesis. For instance I find I love thinking about new directions, new experiments etc, but once I need to just repeat the experiments over and over (tweaking the conditions, but they're basically the same) it starts to feel dull and I stop working on it. GTD has really helped me with this as I can write down literal next actions like "go and get my sample from the furnace and box it up" and "download images from the microscope" and it suddenly all seems much easier - these have replaced my old to-do list with awful non-NAs like "complete experiment 1" - which would probably take me about a month!