Michigan DT Alan Branch is falling because he has two broken legs. Maybe he has stress fractures, maybe he has shin splints, and either way it could cost Branch millions if he falls out of the top 10. He may even fall down to the Packers at pick 16.
I don't know if the Packers should select Branch at 16 over RB Marshawn Lynch if both players are available. As much as the Packers need someone to run the ball on offense they also need someone to stop the run on defense. NT Ryan Pickett played very well last season and remains a solid run stopper, but there is no depth behind him. The Packers run defense could be very suspect if Pickett was hurt. I'm probably a little biased in preferring Branch over Lynch because I remember how Branch dominated the Wisconsin Badgers and helped shut down their run offense during the Badgers only loss in 2006.
FYI - Although Football Outsiders writer Bill Barnwell took a shot at defensive tackles from the Big 10 I stuck up for Pickett in the comments at foxsports.com.