One of the biggest challenges in applying personal informatics in the medical arena lies in the sensing technology needed. Non-invasiveness and automatic data capture are the keys here. Currently there are a few methods that do capture some data this way: electroencephalography, electromyography, galvanic skin response, pulse oximetry, bioacoustic sensors. The Bodymedia Fit device http://www.bodymedia.com/ is of note here, in that it senses skin temperature, galvanic skin response, heat flux and also has an accelerometer. Other sensing technologies are in various stages of development: optical biosensors, implantable sensing chips, carbon nanotube ink.
Non-invasive sensing technology will progress, and as it does, more devices will appear that can capture multiple physiological data. Complete solutions could be designed and customized for individuals. This would go a long way toward bringing personal informatics into the mainstream to affect health outcomes.