I think the Yankees are the team who would most likely make that risk and be able to weather the storm should it backfire. But the BB/9 and K/9 numbers suggest that he has some really good control and "stuff" that might translate well to the MLB. Whoever wants him to play for them while he is young and has the potential to actually improve is going to have to pony up.
While pitching in the same league where Tuffy Rhodes may very well be a Hall of Famer. The same league where Matt Murton is a run producing slugger... breaking Ichiro's record of most hits in a season (in his debut season there). The same league where Fukudome was a former MVP.
We see guys that fail in AAA here, go over there and dominate as pitchers (Gary Glover: 9-3 1.9 ERA in 2009 for one example). In other words, I see NPB stats, and gloss over them as being something of a league higher than the Southern League(AA) or Texas League(AA) and beneath the PCL (AAA).
The one real positive I see here is that Darvish is still quite young. That means he has potential to improve and develop, where guys like both Matsuis, Dice-K, Fuki, Kuroda, Uehara, Ohka, Otsuka, Takatsu... etc did not because of how old they were before being eligible to come here.
The only real successes that have come from Japan have been Ichiro and Nomo for the long term, Kuroda, Saito, and H. Matsui for the short term.