Sharp-eyed Fringe viewers are typically rewarded for their vigilance. For example, you can catch glimpses of the Observers even before they're introduced into the plot. These pale, bald men in suits can often be seen in the in crowds at the scene of strange events that the Fringe Division investigate.
Though the Observers are playing an ever increasing role in the story, we still know almost nothing about them. One of the few things we do know is they possess technology beyond the dreams of Walter Bishop, which recently has been revealed to be the root of their omnipresence in time. That is to say that they actually don't experience time in a linear manner and instead exist at all points in time simultaneously. There just seem to be more questions than answers when it comes to the Observers. Where are they from? When are they from? Why do they watch us? Only time will tell.
