Sitting Step1 in ~6 weeks:
I went through UWorld once during Sept-mid-October --> timed; random; read all of the explanations slowly and annotated accordingly. I then went back and did all of the incorrects over a two-day period. = 1.15 passes.
I'm going to blast through it again over a 7-day period about three weeks-out from the exam, only reviewing marked and wrong answers. At the end of the week, I'll once again go over the incorrects.
= 2 real passes with 2 incorrect-Q-passes = probably 2.20 total passes (based on guessing 5% incorrect wrong the second time through)
The bottom line is that, in my opinion, three passes is too much (means you hadn't learned from it well enough the first time), but two passes alone (without the separate incorrect-Q-passes) doesn't really hit the incorrects as heavily as needed.
Kaputt has pointed out to me though that most of the exam is "bread and butter": focus on high-yield stuff and don't obsess over the obscure UWorld questions.