"...and you may not even know" - huh? Seriously? I thought this is well-known. The privacy implications have been discussed before many times (even Wikipedia knows about it: http://en.wikipedia.org/wiki/Mobile_phone_tracking#Privacy ) It's just that most people don't care enough, or at least they are willing to trade that part of privacy against the advantages of ubiquitous connectivity.
Everyone knows abstractly that cell providers can store all your location information. But the extent and detail that this real data set shows can be an eye opener. The most shocking thing to me is that this information wasn't recorded because he was specifically targeted, but this information is stored for everyone, for such a long time.
The cell companies need data on crowd movements[1] to best allocate network resources, to provide a better service. This collective data has to come from a collection of individual datum. Data might need to be collected for all users over a long time frame (years) to correctly identify (for example) how much additional infrastructure is needed near stadiums in football season, how the profile of commuters is changing and what new suburbs are being inhabited.
If we want a stable and reliable cell network, we have to allow the cell companies best plan for our usage.