While totally true, the question wasn't about how soon is too soon to know someone.
It was more of a magical question: If you knew all the important stuff and had a guarantee this was the right person to marry, would you go ahead and do it? Or do you have the kind of personality that would just hold off because it's a comfortable stage to be in and you wouldn't feel like pushing forward? I meant it more like that.
I see dating (in my limited scope of it) to be like this: The initial getting-to-know-you phase where you're constantly weeding through info for the important stuff, determining compatability. That takes lots of adjusting and compromise. You make the decision to "be together" which takes more adjusting and compromising. Moving in/engaged/married--same thing. That may be one of the reasons many marriages fail within the first couple years IMO. If you're constantly "moving" in the relationship, you're not used to just being in one stage with each other for a long time--and that's pretty much what marriage is so if you haven't "practiced" it you're less likely to succeed doing it. You have to know how to move forward with each other but learning to just hold still with each other is pretty important, too.
Obviously, that's not true of all people whose relationships progress quickly, but that's one aspect I notice. I always thought I was one who'd "just know" and then go for it but maybe that's not me. Because, a couple years ago, what dreamseeker and agzg described would have sounded pointless and avoidant to me. Right now, it sounds pretty fantastic.