95% of mobile phone users leave location data more unique than fingerprints9
One important point to understand is that this study was done before the smartphone became part of everyone's daily arsenal. It also was done in the days before App Stores and apps that required your location. Apps like Twitter, Foursquare and Facebook to name a few, use geo-tagging. This data not only allows you to use certain features of these applications,it also helps advertisers focus a specific campaign on a certain area. It's all benign to be sure, but there is always the fear of abuse. If this study is right, location data could some day provide the "aha" moment in a courtroom. And by the way, this was not a paper done by a couple of morons. This was a project developed by MIT and Belgium's Louvain University.
source: Nature.com, FastCompany via textually.org