In general, it seems like most experts expect the Green Bay Packers to win the NFC North, and their only serious challenger will be the Chicago Bears. It seems like everyone is focused on their offense, and how the Bears will take a step back in 2011. From ESPN:

In reality, the Bears are a deeply-flawed team and last season's success -- including five games won by five points or fewer -- masked Chicago's true deficiencies. This year they will be hard-pressed to duplicate last season, and make it back to the playoffs. 

There are several reasons. But they boil down to the Bears' offensive line issues, a lack of offensive playmakers and several intangibles working against them.

While their offensive line did stink in 2010, they did draft an offensive lineman in the 1st round, and it was so bad last season that it couldn't get much worse. Yet they still managed an 11-5 record and an NFC North championship.

Julius Peppers was a perfect fit for their defense last season, and they should return next season with a similar starting cast. Defense can be inconsistent from year-to-year, and last season their defense only allowed 286 points (4th best in the NFL), so they could have a problem if they allow 375 points (as they did in 2009). While I don't see any reason why their defense should be notably worse next season, the only reason they fall out of playoff contention next season is if their defense takes a step back.