A Dutch website Bluetoothtracker is using Bluetooth sensors to track the movements of Bluetooth devices around the towns of Apeldoorn, The Hague and Haarlem (although only data from The Hague is live at the time of writing).
On the website the (unnamed) owner explains how he started tracking the devices in Apeldoorn,
"I ... set up 5 locations with a little USB bluetooth stick in each location to collect data. There has to be an internet connection at those locations. Therefore I am using locations where my family and friends live. They 'lend' me the space and the bandwidth. To keep the budget low."
Here is the location of someone named Nina at 1.58pm today:
Obviously, scanning people's locations by their Bluetooth devices raises a number of privacy issues (here is a Guardian article discussing this very issue). Blutoothtracking does block names that have first and last names combined, only last names, email addresses, phone numbers, company names, website names and anything else that might be traceable back to an individual. However if you do know Nina (from the screenshot above) it probably wouldn't be too hard to work out that this is her.