According to the folk from the Official Nintendo Magazine, Snaking in Mario Kart Wii is a thing of the past.
The latest edition details the game's mechanics, and had something interesting to say about power-sliding:
The second big difference (in Mario Kart Wii compared to the rest of the series) is the removal of snaking. Ever since the N64 game, practically every Mario Kart game has included the ability to get a speed boost by waggling the controls left and right as you powerslide. This has finally been scrapped, and now your speed boost is determined by how long you can hold the slide.
Snaking can be described as using the powerslide boost to, if pulled off right, gain multiple speed boosts in virtually any part of the track - especially in straight sections.
Thanks to Aussie-Nintendo.