You know I'm not too sure about these things...
"A new feature called "Passing By" will allow your DS to connect automatically with other players that are nearby. As you advance in Black and White, you will be able to help others on their journey."
For one 'helping someone out' could mean so many things, it could mean you walk past someone and they get a present or something rather than anything big.
"There is a new "High Link" feature that is reminiscent of the rescues in the Mystery Dungeon games. You can take on missions from a building in the middle of Isshu to help players who are in trouble."
This High Link sounds confusing, co-op play just sounds out of the idea of Pokémon and I just can't see you popping over to someone elses game to when they say they are stuck...
It might just mean the person you are assisting 'gets' one of your Pokémon to help (like they temporarily get it on their game but you don't lose yours) or some variation on that o.O Kind of like those people you help in DPPt by doubling up with them. :S