First up is returning starters. (This information is from the 2011 Big Ten Football Spring Prospectus)
IowaThe Hawkeyes don't return much in the way of starters--just 5 on offense and defense and a kicker. Iowa has the league low in total and defensive returners and ties with Wisconsin for the lowest number of offensive returners. However, there are many other players coming back with starting experience. Binns started 5 games last year and a bunch in 2009. Gettis and MacMillan both had starts on the offensive line. DiBona, Herman, and Rogers also started at least one game last year. All of those players are likely candidates to start in 2011 (assuming Rogers will get healthy and maybe not so much with DiBona). Still, Iowa is going to be a relatively inexperienced team next year.
The restMichigan and Purdue both return just about everyone. Though neither team was very good last year and Michigan is not returning their head coach. Another team to watch is Northwestern as they return most pieces of their offense.
Ohio State returns a lot of starters as well, however, some of the most important will be watching from home the first 5 games of the season. Wisconsin will also have key players missing from last year, especially on offense as the Badgers only return 5 offensive starters.
Overall, the conference has more experience returning on offense (90) than defense (82). The returning offensive and defensive starters are split perfectly between the Legends and Leaders division with each having 86, though the Leaders have a couple of kickers. So the B1G got the competitive balance thing right, at least this year, from a returning starters perspective.