From the NFL:

After consulting with the Competition Committee and NFL staff, the commissioner said the following will be in effect for all remaining preseason, regular season, and postseason games of the 2009 season:

1. If a ball in play strikes a video board, guide wire, sky cam, or any other object, the ball will be dead immediately, and the down will be replayed at the previous spot.
2. If there is not an on-field ruling that the ball struck an object, the Replay Assistant is empowered to initiate a booth review, including if the event occurs prior to the two-minute warning. If, prior to the two-minute warning, no booth review is initiated by the Replay Assistant, a coach’s challenge is permitted under the customary procedures for such a challenge.
3. In the event the down is replayed:

(a) The game clock will be reset to the time remaining when the snap occurred.

(b) All penalties will be disregarded, except for personal fouls which will be administered prior to replaying the down.

The press release goes on to state that this rule change is limited to the 2009 season, because Rule 3, Section 1 of the playing rules requires interim changes to be reviewed by the Competition Committee for permanency.