He didn't do anything.. Seven Pounds is his worst performed movie since Bagger Vance.. Only 70 million in the US..It may finish with 150 million worldwide but Pursuit of Happyness did 320 million.. I Am Legend did nearly 600 million.. its a long way off from that....
Look at the comparison of Will Smith dramas worldwide numbers:
Six Degrees of Separation: $6,405,918
Legend of BaggerVance: $39,459,427
Ali: $87,713,825
Pursuit of Happyness: $307,071,902
Seven Pounds: $111,005,719 and counting
Whilst I agree, 7P is underperforming for a Will Smith movie, for a WS drama, its doing OK. And I personally, would hardly call it a flop.