Cosmic horizon in the de Sitter space is a sphere, centered at the observer with finite radius where the red shift due to cosmic expansion becomes infinite.
Given that no information can be transmitted from behind the cosmic horizon, I wonder whether any matter can ever pass behind the event horizon, because this will give rise to an information paradox, similar to the black hole information paradox.
The matter approaching the cosmic horizon seems to experience time dilation, so will that time dilation prevent it from crossing the horizon?
To work around the paradox, one have to postulate that the information about outgoing matter should be encoded in the de Sitter radiation.
Answer
Everything Thriveth says in his answer is true. However, I can't help feeling it doesn't quite answer the question.
It is indeed correct that no matter can ever pass beyond the cosmic horizon, when considered from the point of view of us, the observers for whom it exists. In this respect it's exactly analogous to a black hole's horizon, in that (again from our point of view), any object attempting to pass it will instead approach it asymptotically, with its emissions becoming rapidly red-shifted to the point where we can't practically detect them.
My general relativity isn't up to showing this in the case of de Sitter spacetime, but it's a property shared by all horizons. It's easiest to see in the case of a Rindler horizon, which is the horizon seen by a continuously accelerated observer. Consider this diagram (from Wikipedia): 
The straight lines radiating from the origin are the planes of simultaneity of the accelerated observer. No object reaches the horizon until the observer's $t=\infty$.
Of course, an object passing the horizon will notice nothing special because the horizon only exists for the accelerated observer. The same is true for the cosmic horizon. An observer passing a black hole horizon will also notice nothing special, for the same reason.
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