Also see http://swineflu.ushahidi.com/

Ushahidi was designed for this very purpose. From the About Ushahidi page: "Ushahidi, which means 'testimony' in Swahili, is a website that was developed to map reports of violence in Kenya after the post-election fallout at the beginning of 2008... The new Ushahidi Engine is being created to use the lessons learned from Kenya to create a platform that allows anyone around the world to set up their own way to gather reports by mobile phone, email and the web - and map them. It is being built so that it can grow with the changing environment of the web, and to work with other websites and online tools."