1) Frank Gore's efficiency has absolutely plummeted since Kendall Hunter's season ended, as he's being asked to shoulder more of the load and LaMichael James isn't quite up to the task of playing as the #2 in the power running schemes the Niners use.
2) Casey Hayward was the most efficient CB in the NFL this season, but he's typically only on the field in nickel coverage. If SF operates out of a 21/22 personnel grouping with Vernon Davis on the line instead of in the slot, it will keep GB in their base personnel and Hayward off the field. That puts more pressure on Crabtree to perform, but he'll likely be working against Tramon Williams, and that's a big mismatch in SF's favour.
3) GB's best shot at keeping SF off balance on defense is running 10 personnel (4 wide, 1 back) because of depth issues in the Niners secondary. The Niners don't play a lot of dime because there aren't many teams that can go 4-wide, but against the Packers receivers, SF will be forced to play dime coverage over a larger number of plays or they'll be leaving their corners on an island against Jennings/Nelson/Finley/Jones. By playing to their strengths, GB in 4-wide is forcing SF to play a sub-optimal personnel, pulling Sopoaga for Culliver in nickel, bringing in Perrish Cox in dime. Cox is not a very good player...
4) When the Niners are in nickel against 3/4 receiver sets, GB shouldn't be afraid to run the ball as that's when SF has been weakest in stopping the run. Not that the Packers will generate a lot of rushing yards, but as long as SF needs to respect it, Rodgers can gain a bit of time to work when throwing downfield.
5) Aldon Smith generates a sack or hurry on QBs on 9.1% of snaps with Justin Smith in the lineup, but has only managed 4.4% without him in the lineup. We won't know which Aldon Smith is going to show up until we know which Justin Smith will be on the field. The performance of the Packers OL will be key here as well, obviously.