Responce from one of the authors of the MDM paper (Score 1)

We agree that the privacy implications of being trackable are serious. That is why we are developing technology to allow people to control how this imformation is shared. For instance, one can put oneself into "total privacy all the time mode" or "show my presence for the next hour to a client so we can find each other". Fine- grain control of trackability will keep the service useful, rather than intrusive. A big part of the work is on avoiding location-based spam. If you want coupons for a coffee place, you can let them know you are interested during certain times of day or when in certain places. If they abuse it, you turn it off. The point is to restrict the kind of information that can be sent to you to "opt-in" rather than "opt-out". You will not get abusive location-based messages from companies you have not pre-approved if this technology is put in place.