^^
I think that some is due to the rapport that certain GMs have with one another. But from the sense of talking about where trades occur, you are going to get little nuggets of information all around.
As an example, when Boston was chatting with Calgary about the inclusion of the #15 pick, I am certain that the topic of whom the Bruins were interested in came up. As soon as names of players that Calgary had ranked in the #22 and later area came up, you can eliminate certain players from their targets at #15. They may even have stated to the Bruins that they had a group of players from #13-#18 that they were comfortable with, and named a few off to see if the Bruins were targeting similar players. Once it became obvious that the Bruins may have been reaching on players or that those players were further down the Bruins list, Calgary pretty much jumped at the deal. Once the draft is over, it is free to talk further about where they had players, and I am certain that teams will go up to management after the first round and say, "Great pick at #30. We had him at #18 and if you didn't take him, we would try to move up to the top of the 2nd round to get him..."
It is possible that we even had discussions about moving up to 15 long prior, and Calgary said no b/c our specific targets were too close to theirs, and the Flames did not have players at #30 and #32 that they were big enough fans of waiting on...
Makes an interesting thought when you look at a player like Visentin. I think you do wind up getting a feel for certain draft boards, and teams do give some limited information. It is possible that 6 of the next 8 teams in the 2nd round of the 2010 draft had Visentin somewhere between 20 and 40, and while management couldn't pinpoint that spot on the board, it made sense to take the pick there if we had him ranked at #32.