I took it today; just came back from the testing center.
I had the opposite impression, i.e., that the blocks were getting progressively easier. My background is in math/stats and I did some work/research in psychometrics (IRT, latent models) before going into medicine and I had the clearest impression that I was taking an adaptive test (by block).
Right off the bat my first 2-3 questions were insanely WTF and I ended up marking almost 20 questions on my first block; I'm a liberal marker but not that liberal.
Second block was undoubtedly easier, but still an easy 1 sigma above UWorld. Finally, on the third block I started marking about 4-7 questions per block and things seemed "normal". At that moment I was "certain" it was an adaptive test, which was quite a bummer as I "knew" I had screwed up by not setting my score on a higher plateau (in a nutshell, adaptive tests "converge" on your "true" score by changing difficulty as you take the test, or blocks, according to your right/wrong answers). Now, adaptive algorithms should theoretically be able to work both ways, hard->easy or easy->hard, though the former path takes a higher psychological toll, in my view.
That said, as Google make me realize, it seems the USMLE Step 1 Exam is NOT an adaptive test after all. As a matter of fact, as far as I could gather there is virtually no transparency whatsoever about how exams are scored etc. But that's a different thread all together.
In any case, I felt the increased time pressure as well. I usually had 10-18 minutes left in each UWorld block during prep (averaging about 75% correct) and I found myself with about 5-12 minutes left on the real thing.
After taking about 8 or 9 NBMEs (6 online + other offline) my opinion is that those questions are NOT representative of the real exam. Some concepts may be the same, specially in pharm/anatomy/biochem, but the overall "take" is very different. Content-wise, the Online Free 120 seemed the closest, UWorld coming second (I sometimes felt that UWorld question writers try overly hard to come up with super duper clever ways to ask very simple things).
Unfortunately (to me), there were too many anatomy questions to my taste, as well as the usual rote pharm/biochem/immunology/embryology memorization. And I redid ALL UWorld anatomy questions days prior to the exam; and still some 6-8 questions were simply NOT there.
Digression: no wonder Anki cards are the coolest thing. I would really really like to hear what Osler and Cushing would have to say about people claiming they are "learning medicine" by going over 3000 cards per day. End of digression.
But this could be just an heuristic bias as these areas tend to be more "painful" me (coming from math I just can't do memorization; my problem, I know).
As the fellow test taker wrote above, my last 5 blocks were also reasonably decent in terms of difficulty, though I tackled them a little bit more tired than I could have. It is what it is.
To sum up: remember your training, sleep well the night before, keep your glucose level high during the exam and you should be fine. Adrenaline does wonders.
Finally, I think I passed but that's not nearly enough being the non-US IMG that I am (or anyone for that matter). Won't be hitting 250 either but that's fine too.
I'll post all my prep details when results are up on the 22nd. Or not. I wouldn't like to spoil the 260+ SDN average. ;-)
Back to my caipirinha.
