Pokemon has always been one of those games that emphasized collection and connectivity with players. Perhaps the most innovative aspect of Pokemon Black and White fell onto the shoulders of the Pokemon Global Link, the service that allowed players to share items and capture rare Pokemon in the Dream World to bring back to their games. With the sixth generation of Pokemon just around the corner however, Nintendo announced that they will be ceasing Global Link operations for the 5th generation games come January 14th, 2014.
This means that the Pokemon Dream World house, along with all the little extra downloadables not added to your main game, including items and pokemon, will be inaccessible come January. It should be noted, however, that Nintendo is not eliminating the Global Link system fro good, they are simply moving on to the 6th generation games of X and Y, offering a new Global Link with new features. The new Global Link will be released on October 12th, 2013.
So if there was any time to take your wayward Wooper out of the Dream World or capture a rare Spiritomb in the haunted mansion, you have until January to do it.
Source: Pokemon Global Link