I already made an article of this game on TBBT, but I'll make an official topic for it.

Mario & Sonic at the Winter olympics is the continuation of Mario & Sonic at the olympics. The game will be released for the Nintendo Wii console and the Nintendo DS handheld and it is being developed by Sega while published by Nintendo.
Much like its predecessor, the game will revolve around Olympic mini-games. All the characters from the past game will be playable, and do expect newer faces as well.
The game features a 'Festival Mode', which acts out as a story mode in the game; you'll be able to play from opening to closeur of the Olympics. Also, some mini-games will be playable with the Wii Balance board but do not require it. The multiplayer on the Wii will feature a Co-op and competetive gameplay.
The DS's multiplayer counterpart has an 'Adventure tour', were you'll be able accept challenges and battle agaisnt bosses. DS indiviual download is possible for those who wish to play the game in multiplayer but don't own it.
There's still no official release date, so keep listening!