Blinks became synchronized when watching a film of another person, but not when watching landscapes or listening to stories.

Interestingly, blinks seems to be controlled so they occur at the start and end of meaning actions.

This is from the study abstract:

Synchronized blinks occurred during scenes that required less attention such as at the conclusion of an action, during the absence of the main character, during a long shot and during repeated presentations of a similar scene. In contrast, blink synchronization was not observed when subjects viewed a background video or when they listened to a story read aloud. The results suggest that humans share a mechanism for controlling the timing of blinks that searches for an implicit timing that is appropriate to minimize the chance of losing critical information while viewing a stream of visual events.

[via Mind Hacks]