This reminds me of a point I heard someone make about (I think) a Heinlein novel.  Heinlein (or whoever :)) had predicted the widespread use of telephone answering machines.  Their point is that this was kind of easy to do - but what Heinlein also did was predict that people would use them to screen phone calls (in the book, the character hears his Dad call in, and picks up the phone and says something like "I'm in for you, Dad.")<p>The point is that predicting how people will use stuff is the hard part (as you say).