Because people consider their "designated prep time" to be that which lies between the end of MS2 and the Step1 (generally 4-8 weeks), I fall into the category of a long-term preparer because I'll be taking the exam this December, which is one year after my MS2 (Australian academic calendar goes Jan-Nov, not Aug-May, and I finished MS2 Nov 2011).
Those who take the exam "late" (such as me) always have specific reasons for doing so.
I hadn't ever thought about sitting the USMLE until midway through Sem2-MS2 (i.e. I was previously fixated on practicing in Australia), but I had realized at the end of MS2 that I was in no position to perform my best on it, nor had I touched FA or any of the QBanks at that point. My guess is that I would have scored around 190-200 had I taken the exam at the end of MS2 not having prepared for it.
What really struck me initially was when I had gone through the Sanjiv Microcards in December of 2011, after my MS2. My SoM didn't teach micro at all, so when I learned these cards I immediately noticed my feelings of my own competency jump dramatically; the same goes for the Lange pharmacology cards. I also went through Underground Clinical Vignettes - Anatomy in January 2012, which I found to be very helpful.
I spent February reading FA cover-to-cover and did USMLE Rx in tutor-mode in March-April. Doing just those latter two resources alone I had felt to be transformational. I believe I was probably sitting around a high-230, or perhaps just nicking a 240, after I finished Rx. What really shocked me though was that although I had learned a lot since I had finished MS2, I couldn't believe that my school hadn't taught a fraction of the stuff in FA. It reinforced in me that the USMLE isn't just a milestone, it really does ensure that you have a minimal knowledge-base going into medicine. Looking back, I'm scared to think of what things would be like if I hadn't started preparing for the USMLE.
After I finished Rx, I used May to go through FA Q&A, Kaplan QBook and BRS Behavioral Science. I then took a 6-day vacation roadtripping up to Cairns for scubadiving with my mate (also a med student), and on downtime quickly read through Underground Clinical Vignettes - Behavioral Science.
From mid-June till mid-July, my sister got married and I had to fly to New York. Studying was slightly more turbulent during this stage, but I managed to go through GT QBank (not the flashcards; just their QBank) and start a second cover-to-cover pass of FA. From mid-July till the end of the month, I finished the second pass of FA. I sat NBME3 at that point and scored 250.
The next day I started Kaplan QBank. I made all annotations into FA in orange. I used all of August to go through the QBank. I had a few days left at the end of the month that I used to breeze through the questions in the behavioral science and pharmacology Kaplan lecture notes.
September (currently) = UWorld, in green ink. It's going a lot slower than I had previously anticipated, so I'm looking to get it done by late-October. I'll also be looking to through the offline, ungraded NBMEs and old Free-150s before November starts. Once November comes, I'll go back through USMLE Rx and UWorld both for a second time, each at 322 Qs/day (to build a sense of endurance). My exam is December 14th, so the time between my second pass of UWorld and the exam I'll reserve for the rest of the online, graded NBMEs, the recent Free-150 and for memorizing my annotated FA. I'll spread the NBMEs and the Free-150 evenly across those last couple (or few) weeks while reading FA in order to "stay fresh" on questions. Any incorrects from my NBMEs I am transferring into a Powerpoint, which I will review on the day before the exam.
Now the thing is, yeah, this essentially will become a one-year-long prep. On the other hand, there are people on this forum who have their 6-week prep but have still managed to have gone through Gunner Training, FA twice and the major QBanks during their MS2. So in essence, this prep isn't really extended; it's merely remediation for what I hadn't (and was supposed to have) learned during MS1/2. Some people have told me that, after the exam, I will feel as though I had wasted months preparing. In contrast, regardless of the actual score I get, I have learned so much this year that none of these months are wasted in my mind in a million years. The common info is now permanent. The minutiae is now common.
What I can comment on is that, in the beginning, all of the material in FA and the QBanks is just there for you to study, and you'll essentially just feel swamped in it all, not certain at times about how to manage it (like trying to pacify 100 obstreperous children in a school yard). However as the studying progresses, it begins to feel strangely well-contained (first felt this way after Rx), to the point that much of it is merely just behind you and you're ready to move on (definitely feel that way now).