Just for the record, here's the text of the rule from the Official 2012 Rulebook:
Rule 8
Section 2 - Intentional Grounding
Article 1 Definition. It is a foul for intentional grounding if a passer, facing an imminent loss of yardage because of pressure from the defense, throws a forward pass without a realistic chance of completion. A realistic chance of completion is defined as a pass that lands in the direction and vicinity of an originally eligible receiver.
Item 1: Passer or Ball Outside Tackle Position. Intentional grounding will not be called when a passer, who is outside, or has been outside, the tackle position throws a forward pass that lands at or beyond the line of scrimmage, even if no offensive player(s) have a realistic chance to catch the ball (including then the ball lands out of bounds over the sideline or endline). If a loose ball leaves the area bordered by the tackles, this area no longer exists; if the ball is recovered, all intentional grounding rules apply as if the passer is outside this area.
Item 2: Physical Contact. Intentional grounding should not be called if:
(a) the passer initiates his passing motion toward an ineligible receiver and then is significantly affected by physical contact from a defensive player that causes the pass to land in an area that is not in the direction and vicinity of an eligible receiver; or
(b) the passer is out of the pocket, and his passing motion is significantly affected by physical contact from a defensive player that causes the ball to land short of the line of scrimmage.
Item 3: Stopping clock. A player under center is permitted to stop the game legally to save time if, immediately on receiving the snap, he begins a continuous throwing motion and throws the ball directly into the ground.
Item 4: Delayed Spike. A passer, after delaying his passing action for strategic purposes, is prohibited from throwing the ball to the ground in front of him, even though he is under no pressure from defensive rusher(s).