The Internet is not simply being used to search for information about disease and treatment. It is also being used by online disease-focused communities to organize their own experience base and to harness their own talent and insight in service to the cause of achieving better health outcomes. We describe how news of a possible effect of lithium on the course of Amyotrophic Lateral Sclerosis (ALS) was acquired by and diffused through an on-line community and led to participation in a patient-driven observational study of lithium and ALS. Our discussion suggests how the social web drives demand for patient-centered health informatics.