I notice this mostly with the younger generation these days (young women especially). They literally feel the compulsion to always have some sort external stimuli coming in, usually in the form of a constant stream of music from their phones/MP3 players. I remember most of my ex girlfriends being like this, they could rarely be alone with their own thoughts for more than a few minutes.
I genuinely think that a lot of people are afraid of introspection and quiet these days, in fear of what they might find if they look inside themselves or just absorb the world around them in an unprocessed and unaltered fashion. It is just easier to shut down any self reflection our minds might attempt with a constant stream of junk stimulation from the outside.
ADD is becoming a huge problem these days and people's attention spans just keep getting shorter and shorter.