As you've probably heard by now, the basic idea is to look at Google search data as a leading indicator of key developments in public health. Searches about flu indicate increasing flu activity. Pretty simple stuff.
"So why bother with estimates from aggregated search queries? It turns out that traditional flu surveillance systems take 1-2 weeks to collect and release surveillance data, but Google search queries can be automatically counted very quickly. By making our flu estimates available each day, Google Flu Trends may provide an early-warning system for outbreaks of influenza."
I have no intention of entrusting my information to Google health, but I think this is pretty cool stuff that doesn't quite yet cross the line into violating user privacy (but could pretty easily).
In the meantime, flu activity in Massachusetts is currently low. Whew.