I recently come across BodyTrace, a nice way to combine a bathroom scale that wirelessly uploads and displays your weight and BMI and a website where you can track all the changes with visualized solutions. An excerpt from the description:
We are using the GSM network to transmit your weight to our website. We use these measurements to create weight and BMI charts and by combining this information with additional data that we collect (from food tracker, for example) we can better evaluate your progress and give you feedback on how to reach your goals.
See more examples of how Web 2.0 or social media can be used in fitness here.
*This blog post was originally published at ScienceRoll*