TechCrunch reports on Google’s location history browser.
If you carry any Google-filled gear (like, say, an Android phone or tablet), there was a prompt during the initial setup that asked if Google could transmit your location data back to the mothership. This is that data. You know how Google Now can auto-magically figure out where you work and warn you about traffic? This is the data that makes that possible (or at least a good chunk of it.)
If you are using an Android device and cannot remember if you agreed to send your location data, check this link to see if Google is tracking your location. Unfortunately, Google does not have any of my location history so I will appreciate it if you can share your experience. Do you find it awesome or creepy?