Also, If the DM uses the rules interpretation that falling through threatened areas and other involuntary changes to position do draw AoOs, the victim is extra boned. The Character knocked flying will suffer an AoO from all who threaten it, including the critter who just delivered the awesome blow.
Awesome Blow [General, Fighter]
Prerequisites Str 25, Power Attack, Improved Bull Rush, size Large or larger.
Benefit: As a standard action, the creature may choose to subtract 4 from its melee attack roll and deliver an awesome blow. If the creature hits a corporeal opponent smaller than itself with an awesome blow, its opponent must succeed on a Reflex save (DC = damage dealt) or be knocked flying 10 feet in a direction of the attacking creature’s choice and fall prone. The attacking creature can only push the opponent in a straight line, and the opponent can’t move closer to the attacking creature than the square it started in. If an obstacle prevents the completion of the opponent’s move, the opponent and the obstacle each take 1d6 points of damage, and the opponent stops in the space adjacent to the obstacle.