Wii Fit is to be released in North America sometime in 2008 (presumably earlier rather than later, but there’s no way to know). Here’s excerpts from a preview along with an official trailer and screenshots for Wii Fit.
“Nintendo’s goal with [the] Wii is to attract [as] wide [of a] range of people to [play] Wii by using the system’s unique features, such as the motion control. Many of Nintendo’s games released for Wii have thus [far] seemed to incorporate motion control, and gamers seem to love it! Rather [than] swinging the Wii Remote to hit a tennis ball or pointing and clicking the Wii Remote to choose a correct answer, [players will use the new Wii Balance Board to play Wii Fit.“-Snoopdogga (full preview)

Playing a push-up game in Wii Fit.

Trying to balance perfectly in Wii Fit.