Not sure if we’ve covered this, but Intel’s Jabberwocky apperently lets you war-walk with your bluetooth cellphone.  It remembers who you’ve seen and at what time, so you can see if there’s a particular stranger who you encounter everyday.

I’m not sure if I would consider this to be an invasion of my privacy, since no single entity is persistently tracking me.  But if they uploaded this data and aggregated it…