FanGraphs, through the use of pitch f/x data provided by Major League Baseball, attempts to measure the effectiveness of certain pitches. According to their data, Vazquez saw an across-the-board jump in the value of all four of his pitches (fastball, curveball, slider, changeup). Clearly, the use of his curveball was only one part of Vazquez's improvement in 2009.
Yet, no pitch in Vazquez's arsenal saw as much of a drastic bump in value as his curve, which according to FanGraphs ranked as one of the game's nastiest.
Vazquez's curveball saved a career-high 17.2 runs above average last season, putting him behind only the Astros' Wandy Rodriguez (23.9) and the Cardinals' Adam Wainwright (23.3).
Javier Vazquez may be one of the key factors in whether or not the Yankees can take the AL East. While expecting him to repeat last year where he was one of the best pitchers in baseball is probably not realistic, If he can give the Yankees 200 innings of 3.50 - 4.00 ERA I'd have to think the Yankees would be in the driver's seat for the division title.
If last year's success is actually due to a change in approach, ie using his curve more often, it bodes well for 2010.