Nintendo announced overnight that as of May 20, the company will end online functionality for a host of Wii, DS, and DSi games--including high-profile titles like Mario Kart Wii and Super Smash Bros. Brawl. Of course, you can still play the games in their offline mode, but you won't--come May 20--be able to play online or access leaderboards.
Wii Speak and the Wii Speak Channel are also affected, as they require an Internet connection.
Online play for Wii U and 3DS games is unaffected (outside of the Wii mode on Wii U and DS games played on 3DS). Other online functionality, including access to the Wii Shop Channel, the Nintendo DSi Shop, and video-on-demand services like Hulu and Netflix, is also not affected.
"We at Nintendo sincerely thank our fans for their continued support of our company's legacy systems," Nintendo said in a statement. "Your enthusiasm for games made for these systems speaks to their longevity, and the passion of Nintendo fans."
Though the closure of online support for games might come as a headache for some players, sunsetting online services for aging titles is nothing new and it is not a practice conducted exclusively by Nintendo. Publishers often need to end online support for older titles so their IT staff can focus on supporting new games, which need more attention.