I can't remember which commenter (sorry) mentioned this, but I believe it was yesterday he compared MY's average HR distance and speed off the bat from last year to this year. Both were up this year. I figured it was just related to him bulking up some or a small sample size.
Then I ran across this article and here's the money quote:
So, very early this season (actually on the second full day of games), I had already noticed that balls were seemingly flying farther than they usually do, so I checked my numbers, and noticed that the standard distances of all the home runs around MLB were a lot longer than those hit in 2008. Since then, I’ve continues tracking this, and what was little more than a feeling and some numbers off a very small sample size have become a lot more compelling: the first 350 home runs this year are flying, on average, about 6 feet farther than last year. The likellihood that such a difference could come about by chance is exceedingly low, less than 0.0031% the last time I ran the stats on that. I’ve tried to come up with some other possible ways that league-wide homers could be flying so much farther, given that the weather is already factored out, and the ball is the most likely explanation.