I've just spent the past week in Tokyo and not seen one person twittering away like I usually see in the states. They tended to be talking or checking email, not typing "i just finished eating, looks good!" into the ether...
This is more like the dream of what some extremely closeted Americans might think Japanese youth are into.
Side comment: when this was announced, I tried to post the cover because it sounded like such a ridiculous title and could not get the cut right based on the info in the instructions so ended up deleting the post. Is there a super-dummies guide somewhere?