2008: 28 years old, 14 Rbat, .292 ISO, 15.6 Whiff %:
2009: 29 years old, 33 Rbat, .292 ISO, 15.7 Whiff %
2010: 30 years old, 19 Rbat, .229 ISO, 14.6 whiff %
2011: 31 years old, 17 Rbat, .235 ISO, 14.5 whiff %
2012: 32 years old, -6 Rbat, .204 ISO, 15.2 whiff %
2013: 33 years old, 3 Rbat, .201 ISO, 16.5 whiff %
He hasn't been hitting really any balls between the right-fielder and center-fielder, and most of his pulled balls are not hard pitches. Most of those are hit the other way (along with breaking pitches, which makes sense, as most breaking pitches are thrown to the glove side of the plate by pitchers that have the platoon advantage, meaning they would be on the outside to Howard or any hitter).
The problem isn't up and in, as Howard still has power up there, hitting a couple of homers on up and in pitches in the zone (he only had 2 in that zone, zone 3 according to Baseball Savant, in 2008). The problem is low and in (zone 9). He has 19 swinging strikes on pitches low and in so far in 2013. In 2008, he had 15 in that zone in a much bigger sample size.
Since 2008, he has 97 whiffs on pitches 95 MPH or over (16.1%). 26 of them have come in 2012 or 2013, even though his 2012 and 2013 seasons represent just 18.3 % of pitches seen since 2008 for Howard. There has been a clear bat speed regression for Howard, and this season, it is letting pitchers come more inside.