As per the Baseball America Minor League Transactions page, the Pirates have released the following 6 minor leaguers:
RHP Brandon Holden, RHP Brent Klinger, C Joey Schoenfeld, 1B Billy Nowlin, OF Ping-Hung Chi, OF Daan Cornelissen
Brandon Holden was a 13th round draft pick out of high school in the 2006 draft. He was plagued by injuries throughout his career, but the Pirates saw enough potential to keep him around this long. He had not pitched anywhere yet in 2011.
Brent Klinger was a 21st round draft pick in 2008 and was also injury-plagued. He has not pitched for a Pirates' affiliate since 2009.
Billy Nowlin was a free agent signed a few weeks ago to fill in at State College.
Ping-Hung Chi was a free agent signed in 2009 from Taiwan. There is no truth to the rumor that the Pirates actually tried to release him last week, but couldn't find him because he's so small.
Daan Cornelissen was a free agent signed in 2009 from the Netherlands.