Is Dunn being too selective? That's kind of a philosophical question. The first question should be: Are there any significant differences in Dunn's 2010 statistics when compared to the rest of his major league statistics?
The percentage of pitches Dunn has swung at in 2010 is basically in line with his career averages. Same thing for his contact percentage so far. Dunn is also putting about the same percentage of balls in play that he always has. And he's not really striking out at a higher rate either.
What is different is that Dunn is swinging at more pitches outside the strike zone and taking more pitches inside the strike zone.
Pitchers in 2010 have given Dunn less to swing at in the strike zone. Is this leading a frustrated Dunn to go reaching at pitches outside the strike zone? Maybe Dunn is being too selective when it comes to pitches in the strike zone and not being selective enough when he swings at pitches outside the strike zone? I don't know; I'm a blogger, not a hitting coach. But it's an interesting data point. Another interesting data point, at least for those who are frustrated when they watch Dunn take a called third strike: Dunn's Strikeout Looking Percentage in 2010 is the lowest in his major league career.
Anyway, at just one month into the season, it's probably too soon to tell what, if anything, might be wrong with Dunn's approach at the plate. And based on the numbers so far, I might be more concerned with his batted ball data.
(I wish I could do something with all this, but I'm hopeless when it comes to generating Pitch F/X charts and using Excel.)