Amazon.com Product Features:

• Lean to block soccer balls, swivel hips to power hoop twirls or balance to hold the perfect yoga pose. As you stand on the Wii Balance Board, included with Wii Fit, your body’s overall balance is tied to the game in a way you’ve never experienced before.
• Wii Fit also uses the Wii Balance Board for daily tests. These evaluate two key measures that a household can track via progress charts -
  Body Mass Index (BMI) – A weight evaluation based on a ratio of weight to height.
• Wii Fit Age – The Wii Fit Age is measured by factoring the user’s BMI reading, testing the user’s center of gravity and conducting quick balance tests
• Wii Fit includes more than 40 types of training activities designed to appeal to all members of a household. Training falls into four fitness categories.

I am sure the Nintendo Wii Fit availability will be similar to the Wii when it first came out, with no one could get one in a decent time period.  I am ordering my Wii Fit tomorrow so I won’t get left calling all over town trying to scrape one up.