The Pokemon Global Link(PGL) was delayed due to the natural disasters in Japan, it was scheduled to launch March 30th but its been re-scheduled to launch on the 13th of April. The PGL is a online website where you can connect Pokemon Black/White to enter the Dream World and participate in some battles.
To use the PGL you need a Pokemon.com account and a copy of pokemon black/white to fully enjoy all the extras
DREAM WORLD The Dream World is a online realm which you and your pokemon can decorate your house, access other people's houses and add a few friends. You don't need a copy of black and white to enter you can use a demo version which allows you to use Dream World with a pokemon called 'Munna'.
If you do have a copy of pokemon black/white then you can send items and pokemon from the dream world which can be collected in the Entralink in pokemon black/white.
Unfortunately the Dream World can be only be used evry 24 hours from when you used it last, i think Nintendo made it that way to reduce the lag in Dream World due to the excessive amount of people on it and some pokemon can't even access it due to not having the Dream World ability.
Well come on guys make a pokemon.com account and have some fun on the PGL its so worth it!