In a move that is as inevitable as it is depressing, Nintendo has decided to shutter Wii and DS online functionality on May 20th. This includes all games, from Super Smash Bros Brawl to Pokemon Diamond and Pearl. This makes perfect sense considering Mario Kart 8 is coming out days after, and Ninty probably wants to have the incredibly large player base of people who play Mario Kart Wii still to pick that up.
There will still be a few things left running on your DS and Wii, however. You can still use the Internet Channel or DSi Browser, and the Youtube and Hulu apps will still work. You can also still buy games on the Wii or DSi Shops. If I were you, I’d get those last Mario Kart and Smash Bros matches in while you can!