Any details of what this actually is have been kept in the dark, until now. Stephen Totilo of MTV Multiplayer has uncovered a description of Mr Wong's Laundromat on a page that has now been removed pertaining to the technology that will be behind this feature.
The feature will be, apparently, a flash application on the web that will allow you to earn cash, and then be able to spend it in GTA: Chinatown Wars.
"Once at the Rockstar Social Club, registered users can also play Flash games like Mr Wong’s Laundromat to unlock additional cash that can be spent back in the game. GameSpy’s custom work links money earned out of game straight back into your in-game funds to spend on bigger guns and more ammo (and you can never have enough of that)."
More information on this to come.
Source: MTV Multiplayer