Sponichi has a list of quotes from Yu Darvish over the years regarding his thoughts on the Majors.
They are as follows:
12/17/2004 (after signing with the Nippon Ham Fighters out of high school while being courted by as many as five MLB teams) - I decided I want to play in Japan from the very start.
9/16/2007 (during a TV show appearance) - If it ever got to the point where I had to go the Majors, I'd quit baseball. In order for me to give Japanese kids a fun time, I need to stay in Japan.
11/23/2008 (during a fan festival) - I've often been asked if my goal was the Majors. I don't think that's the case. I haven't even dream about it.
3/26/2009 (after returning to Japan after the WBC) - I didn't go to the WBC in order to gain approval from the Majors.
9/20/2009 (during a CNN interview) - Japanese players playing in the US, like Ichiro, Matsui, and Matsuzaka, do provide me with stimulation / encouragement, but they don't necessarily make me want to go to the States.
11/17/2009 (during the WBC awards ceremony; when asked if he would be playing in the next WBC as a MLBer) - I think that's enough with those kinds of questions.
His most recent quote went something like this:
Well, I'm just taking things one step at a time. I plan on climbing up the steps to reach the top.