The Wii Fit offers for a low cost price a simple platform with four measuring sensors and can be used with very little effort as a simple and inexpensive force plate, even without the corresponding game console. Clark et al. (2010) suggested that the Wii Fit balance board could represent a valid cheap solution to measure standing balance. Furthermore they have recently suggested the use of the infrared cameras in the hand controllers as a possible alternative to expensive timing light systems (http://www.jsams.org/article/S1440-2440(10)00913-8/abstract). Recent work from Young et al. (http://www.ncbi.nlm.nih.gov/pubmed/21087865) also suggests the possibility of using this technology for developing bespoke diagnostic or training programmes that exploit real-time visual feedback of current Centre of pressure position.
The Wii Balance Board is certified for 300 pounds (136 kg) in Japan and 330 pounds (150 kg) in the U.S. The Wii Balance Board has four sensors, so each sensor is certified for up to 136 kg / 4 = 34 kg per sensor in Japan or 150 kg / 4 = 37.5kg per sensor in the United States.The following Wii Balance Board calibration information from WiiBrew will make more sense.
If you are interested in Linux, you can see here how to extract the force data. I am sure this is not something useful to measure high performance athletes. However it could represent a fun and simple tool for diagnostic measurements in some populations.
If you have one and are able to use it for this purpose let me know!