yeh it was a very obvious part of the scene. As this seems to be an important location on the island. A landmark where stuff with rouseau n the others couldve happened before. Definitely a kind of dark territory there with the others n everything. There is a lot of symbolism continuously used with black and white in the show, and this may be a second 'black rock' location as well as the ship.
as the camera pans around jack you can see a second smaller black rock on the other side of kate, and this could back up the claim that its just another black rock on the island, and theres loads of them. It could also be making 'the line' with the other rock. Whatever it is, that very big black rock as quite clearly been placed in that position right in view (and in focus) of the camera for us to see. Im sure we'll find out sumtime. However i didnt really believe that it was the same location as before, in the hunting party, i know it was dark n everything but there did seem to be a lot more trees around before, that the others were stood behind..

I think that this location will be the point of a big end of series event, maybe a bit of a battle between the losties n the others. black and white. (but which ones which...)