The other day, I read in Sanspo that 2008 Central League Rookie of the Year Tetsuya Yamaguchi played in the American minor leagues. I knew that he was the first former instructional player to win an RoY, but I figured he was from the independant leagues or something and didn't bother to research it further. But it turns out that Yamaguchi played three seasons in the Arizona system, never rising above rookie ball.
The irony is that he won the award for the Yomiuri Giants, so they directly benefited from having a returning Japanese player on their team. Maybe they'll re-think the returnee rule later on.