Here is what Baseball America said about him in their 2008 prospect book. He was ranked 13th in the Cards organization.
Mather reached Class A in 2004, and for three seasons and more than 1,000 ABs, he stayed at that level, wondering each spring if he was making progress or about to be released. Cardinals officials recognized the potential in his swing, and in 2007 he blossomed. He hit 31 HRs as he climbed to Double-A and then Triple-A. Mather used to gobble ice cream and other high-calorie delights to pack weight on his lithe frame. By last year, he had filled out by 15 lbs and his game matured. Scouts saw the same raw ability in Mather, but they wondered if he would ever add the necessary polish. He put it together when he settled into a comfortable stance and approach at the plate, which led to better strike-sone awareness and more consistent power to all fields. He now has the best power in the system this side of Colby Rasmus, and he doesn't strike out excessively for a slugger. Mather is no burner but has stolen 23 bases without being caught over the last three seasons. He may be better at first base, but he runs well enough ans has enough athleticism and arm strength to play a corner outfield position. The versatility that once kept him playing while he struggled with the bat now opens an alternative avenue to the majors, and he's now just a phone call away. Added to the 40-man roster in Novemeber, he'll probably open 2008 in Triple-A.