I have an article up at Baseball Prospectus in their Baseball ProGUESTus column. One of two projects I've been working on lately. I was curious if there was really any difference in how prospects are treated from the rest of the population of players.
Using 2010 MLB debuts vs. the rest of the field, my general finding is that pitchers have a pretty good scouting report early on for players. The approach doesn't change much throughout that first season, bringing to question articles claiming that a young guy got suddenly "figured out" after a hot start to the season. The analysis is pretty macro-level, so that's not to say this doesn't happen. And I only used 2010 data for now. But in the end, the groups of hitter types that a younger player falls into is pretty much known when he reaches the Big Leagues.