Santana was in the line of the many conversion projects that the Dodgers like to undertake, and played just 3 games at catcher over his first two years in the Dodgers system. Over those two years, he split time between rookie ball and Hi-A, oddly enough, and showed an advanced approach at the plate, walking and striking out 69 times each over 488 plate appearances. He showed enough power to stay at a middle infield position, but wasn't much of a corner player based on his level of production. He was mighty old for rookie ball, too.
He spent 2007 learning how to catch, and his offense took a major hit as a result. He spent 2007 in A Ball and he combined to post just a .688 OPS, though he was hurt miserably by a .243 Batting Average on Balls in Play, which is supremely low for anyone, particularly a guy who is not of lead feet. There still wasn't a ton of power, but he was still raw and learning a new position, as catchers generally come along slowly. If I wrote about prospects then, I would have predicted a return to form in 2008.
He split 2008 between the Dodgers and Indians farm systems, and spent the entire time at Hi-A, slighting 8 AB's at AA to end the season. He busted out offensively, posting a .999 OPS with 21 HRs, and 85 BB to 89 K. He stole 10 bases and threw out 27% of the baserunners, which, while not great, is certainly passable. There was no guarantee that the power would return again in 2009, but Santana was a pretty sure bet to demonstrate excellent contact skills and a strong ability to take a walk, which is enough in itself to make it as a catcher in the big leagues. How he was thrown into a deal for a free-agent to be Casey Blake is beyond me.
He's opened 2009 by posting a .909 OPS in 109 plate appearances at AAA. He's got a .267/.404/.535 line so far, which is excellent when you consider that his Average on Balls in Play is a below-average .263. One would expect his batting average to normalize closer to .285, which would raise his numbers even further. He is walking nearly 19% of his plate appearances while striking out in less than 14% of them. He has posted career highs in Isolated Power and in Line Drive Percentage, which our both good signs. I just can't find something I don't like, as it looks like he's developing into a monster, elite top prospect. There is plenty of justification to move him up further on my list, and upon review I just might.
If you're interested in an analysis of Santana's swing, take a look at Baseball Intellect.