SickCity uses mentions of terms such as "flu" "sore throat" and "feeling ill" on Twitter to track outbreaks of illness in a given city. Similar to Google Flu Trends, yet different in that GFT tracks only the US at the State level, while SickCity shoots for a more local level, and worldwide. Right now they've only got cities hard coded, but it looks like in the future you'll be able to add your location to track.
The front page of SickCity shows the "ten sickest cities" but that obviously would match up with cities with high populations of twitter users; it'd be nice to be able to filter by population or # of registered twitter users in a given city to do a true comparison. Looks like Calgary's feeling pretty good these days though. Probably not hugely accurate, but a pretty interesting project. Oh, and they say that soon Facebook will be added into the mix.