I've watched everything I can find of Dice-K (what else is there to do in the offeason, right?). I think the theory about adjusting to a new ball is spot on. He is missing badly with a lot of the pitches that, in Japan, I think were unbelievable breaking pitches. These include the change up (which he has missed up and away to lefties by miles on a consistent basis) and a pitch that I think he tries to throw down-and-in to lefties but which has consistently either gone to the backstop or bounced 10 feet in front of the plate. He got these pitches over in Japan and they were mystifying.
Whoever said it above was right, this has all the marking of Beckett's trip into the AL last year. He is learning how to pitch to hitters.
It is also important to remember that Tek is still learning how to use daisuke and how to maxamize his pitches. There are some pitches that you just have to get over, and some where you can be more aggressive. It is very hard to do, as a rookie, in a new country, with a pitching coach who can't speak your language, under the most intense media coverage imaginable. Baring injury I think most people are pretty confident that he will figure out what he's doing and how to be effective. Right now he's the 3rd best pitcher on the team, but with what he's shown at times he could be the best by the playoffs (if we get there).